U.S. patent application number 15/990648 was filed with the patent office on 2018-09-20 for chemically coded quantum emitters and photochemical methods of creating same.
This patent application is currently assigned to University of Maryland, College Park. The applicant listed for this patent is Mijin Kim, Hyejin Kwon, YuHuang Wang, Xiaojian Wu. Invention is credited to Mijin Kim, Hyejin Kwon, YuHuang Wang, Xiaojian Wu.
Application Number | 20180265779 15/990648 |
Document ID | / |
Family ID | 63521186 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180265779 |
Kind Code |
A1 |
Wang; YuHuang ; et
al. |
September 20, 2018 |
Chemically Coded Quantum Emitters and Photochemical Methods of
Creating Same
Abstract
The present invention relates to quantum emitters and
photochemical methods of creating such emitters, including
semiconductor hosts comprising chemically incorporated fluorescent
defects.
Inventors: |
Wang; YuHuang; (Laurel,
MD) ; Wu; Xiaojian; (College Park, MD) ; Kwon;
Hyejin; (Greenbelt, MD) ; Kim; Mijin; (Silver
Spring, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wang; YuHuang
Wu; Xiaojian
Kwon; Hyejin
Kim; Mijin |
Laurel
College Park
Greenbelt
Silver Spring |
MD
MD
MD
MD |
US
US
US
US |
|
|
Assignee: |
University of Maryland, College
Park
College Park
MD
|
Family ID: |
63521186 |
Appl. No.: |
15/990648 |
Filed: |
May 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15590397 |
May 9, 2017 |
9983058 |
|
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15990648 |
|
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62333372 |
May 9, 2016 |
|
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62595368 |
Dec 6, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B82Y 10/00 20130101;
C09K 11/0827 20130101; B82Y 15/00 20130101; B82Y 40/00 20130101;
C09K 11/65 20130101; C09K 11/06 20130101; H01L 51/0048 20130101;
H01L 51/0098 20130101; H01L 51/0049 20130101 |
International
Class: |
C09K 11/65 20060101
C09K011/65; C09K 11/06 20060101 C09K011/06; C09K 11/08 20060101
C09K011/08 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support by the
National Science Foundation (NSF) under CHE1507974 and CHE1055514;
by the National Institutes of Health (NIH) under 1R01GM114167; and
by the Air Force Office of Scientific Research (AFOSR) under
FA95501610150. The United States government has certain rights in
this invention.
Claims
1. A quantum emitter, comprising: a semiconductor host; a
fluorescent quantum defect incorporated into said semiconductor
host via optically reacting said semiconductor host with a molecule
comprising a photochemically activatable moiety that generates a
radical that covalently bonds to said semiconductor host.
2. The quantum emitter of claim 1, which comprises a plurality of
fluorescent quantum defects spatially, chemically and/or
electronically correlated in said semiconductor host.
3. The quantum emitter of claim 1, wherein said semiconductor host
is selected from the group consisting of a carbon nanotube (CNT), a
graphene nanoribbon, and a carbon nitride.
4. The quantum emitter of claim 3, wherein said carbon nanotube is
a single-walled carbon nanotube (SWCNT) or a double-walled carbon
nanotube (DWCNT).
5. The quantum emitter of claim 4, wherein said carbon nanotube is
a SWCNT selected from the group consisting of a (6,5)-SWCNT, a
(10,6)-SWCNT, a (10,9)-SWCNT, a (10, 3)-SWCNT, a (6,4)-SWCNT, and a
(7,5)-SWCNT.
6. The quantum emitter of claim 1, wherein said molecule is a
halide-containing molecule.
7. The quantum emitter of claim 6, wherein said halide is iodine,
bromine, or chlorine.
8. The quantum emitter of claim 1, wherein said molecule is an
oligonucleotide.
9. The quantum emitter of claim 8, wherein said oligonucleotide is
a DNA molecule or an RNA molecule.
10. The quantum emitter of claim 8, wherein said oligonucleotide
comprises at least one 5-IododexoyUridine (5I-dU).
11. The quantum emitter of claim 8, wherein said oligonucleotide
comprises between 1 and about 1000 nucleotide residues.
12. The quantum emitter of claim 11, wherein said oligonucleotide
comprises between 3 and about 100 nucleotide residues.
13. The quantum emitter of claim 12, wherein said oligonucleotide
comprises between about 5 and about 20 nucleotide residues.
14. The quantum emitter of claim 10, wherein said oligonucleotide
comprises a sequence selected from the group consisting of: SEQ ID
NO: 2; SEQ ID NO: 3; SEQ ID NO: 4; and SEQ ID NO: 5.
15. A photochemical method of synthesizing a quantum emitter,
comprising the step of: irradiating a solution comprising a
semiconductor host and a molecule comprising a photochemically
activatable moiety, thereby exciting the semiconductor host and
reducing the molecule to generate a radical, wherein the radical
covalently bonds to the semiconductor host to create a fluorescent
quantum defect thereon.
16. The photochemical method of claim 15, wherein said step of
irradiating comprises exposing the solution to radiation having a
wavelength of between about 100 nm and about 1400 nm.
17. The photochemical method of claim 15, wherein said step of
irradiating comprises exposing the solution to visible light.
18. The photochemical method of claim 17, wherein the visible light
has a wavelength of 565 nm, 765 nm, 892 nm, or 644 nm.
19. The photochemical method of claim 15, wherein said step of
irradiating comprises exposing the solution to radiation having a
wavelength that resonates with an electronic transition(s) of the
semiconductor host.
20. The photochemical method of claim 15, wherein said step of
irradiating comprises exposing the solution to ultraviolet
radiation or near-infrared radiation.
21. The photochemical method of claim 15, wherein a plurality of
fluorescent quantum defects is created in the semiconductor
host
22. The photochemical method of claim 21, wherein said step of
irradiating comprises exposing the solution to patterned radiation,
thereby creating a spatially patterned array of fluorescent quantum
defects in the semiconductor host.
23. The photochemical method of claim 15, wherein the molecule
comprises at least one halide and aromatic moieties, and wherein
the at least one halide is directly bonded to at least one of the
aromatic moieties.
24. The photochemical method of claim 23, wherein the at least one
halide is selected from the group consisting of iodine, bromine,
and chlorine.
25. The photochemical method of claim 23, wherein the aromatic
moieties are selected from the group consisting of benzene,
aniline, nitrobenzene, and benzene sulfonic acid.
26. The photochemical method of claim 15, wherein the molecule
comprises at least one halide and aromatic heterocycles, and
wherein the at least one halide is bonded to at least one of the
aromatic heterocycles.
27. The photochemical method of claim 26, wherein the at least one
halide is selected from the group consisting of iodine, bromine,
and chlorine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY
[0001] This application is based on U.S. Provisional Patent
Application Ser. No. 62/595,368, filed Dec. 6, 2017, and a
continuation-in-part of U.S. application Ser. No. 15/590,397, filed
May 9, 2017, which application is based on U.S. Provisional Patent
Application Ser. No. 62/333,372, filed May 9, 2016, titled
"Molecularly Tunable Near-Infrared Emitters and Methods of Creating
the Same," all of which applications are incorporated herein by
reference in their entireties and to which priority is claimed.
REFERENCE TO SEQUENCE LISTING
[0003] This application includes one or more Sequence Listings
pursuant to 37 C.F.R. 1.821 et seq., which are disclosed in
computer-readable media (file name: 2105_0066US2_SeqList_ST25.txt,
created May 25, 2018, and having a size of 1,839 bytes), which file
is herein incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0004] The present invention relates to quantum emitters and
photochemical methods of creating such emitters, including
semiconductor hosts comprising chemically incorporated fluorescent
defects.
BACKGROUND OF THE INVENTION
[0005] The excited states of many semiconducting nanostructures,
such as carbon nanotubes (CNTs), are characterized by excitons,
electron-hole pairs bound by Coulomb interactions (Wang, F. et al.
(2005) "The Optical Resonances in Carbon Nanotubes Arise from
Excitons" Science 308:838-841). Excitons are hydrogen-atom-like
quasi-particles, each carrying a quantum of electronic excitation
energy. An exciton can return to the ground state by emitting a
photon, producing photoluminescence (PL), or by falling into a
"dark" state from which the energy is lost as heat. The ability to
control the fate of excitons and their energy is crucial to imaging
(Hong, G. et al. (2012) "Multifunctional in vivo vascular imaging
using near-infrared II fluorescence," Nat. Med. 18:1841-1846; Chan,
W. C. W. & Nie, S. (1998) "Quantum dot bioconjugates for
ultrasensitive nonisotopic detection," Science 281:2016-2018),
sensing (Heller, D. A. et al. (2006) "Optical Detection of DNA
Conformational Polymorphism on Single-Walled Carbon Nanotubes,"
Science 311:508-511), photovoltaics (Kamat, P. V. (2008) "Quantum
dot solar cells. Semiconductor nanocrystals as light harvesters,"
J. Phys. Chem. C 112:18737-18753), lighting and display (Shirasaki,
Y. et al. (2013) "Emergence of colloidal quantum-dot light-emitting
technologies," Nat. Photon. 7:13-23), and many other electronic
applications.
[0006] Over the last few decades, two primary approaches have been
developed to tailor the exciton properties within a
nanocrystal--quantum confinement and doping. Quantum confinement
has motivated the development of many synthetic approaches that
control the size and shape of nanocrystals, and consequently their
electronic and optical properties (Rossetti, R. et al. (1983)
"Quantum size effects in the redox potentials, resonance Raman
spectra, and electronic spectra of cadmium sulfide crystallites in
aqueous solution," J. Chem. Phys. 79:1086-1088; Alivisatos, A. P.
(1996) "Semiconductor clusters, nanocrystals, and quantum dots,"
Science 271:933-937; Yin, Y. & Alivisatos, A. P. (2005)
"Colloidal nanocrystal synthesis and the organic-inorganic
interface," Nature 437:664-670). Doping modifies the electronic
structure of the host crystal and the examples include
nitrogen-vacancy in diamond (Gruber, A. et al. (1997) "Scanning
confocal optical microscopy and magnetic resonance on single defect
centers," Science 276:2012-2014) and metal ion-doped nanocrystals
(Erwin, S. C. et al. (2005) "Doping semiconductor nanocrystals,"
Nature 436:91-94).
[0007] In the case of single-walled carbon nanotubes (SWCNTs), the
excitonic properties depend on both the diameter and chiral angle
of each nanotube crystal, collectively known as chirality, which
may be denoted by a pair of integers (n,m) (see O'Connell, M. J.
(2002) "Band Gap Fluorescence from Individual Single-Walled Carbon
Nanotubes," Science 297:593-596; Bachilo, S. M. (2002) "Structure
Assigned Optical Spectra of Single-Walled Carbon Nanotubes,"
Science 298:2361-2366). It has recently been demonstrated that the
optical properties of SWCNTs can be modified by doping with oxygen
(Ghosh, S. et al. (2010) "Oxygen doping modifies near-infrared band
gaps in fluorescent single-walled carbon nanotubes," Science
330:1656-1659) or by the incorporation of defects through diazonium
chemistry (Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem. 5:840-845). These defects can induce a new near-infrared
emission (Ghosh, S. et al. (2010) "Oxygen doping modifies
near-infrared band gaps in fluorescent single-walled carbon
nanotubes," Science 330:1656-1659), brighten dark excitons (Piao,
Y. et al. (2013) "Brightening of carbon nanotube photoluminescence
through the incorporation of sp3 defects," Nat. Chem. 5:840-845),
facilitate up conversion (anti-stoke shift) (Akizuki, N. et al.
(2015) "Efficient near-infrared up-conversion photoluminescence in
carbon nanotubes," Nat. Commun. 6), and stabilize trions at room
temperature (Brozena, A. H. et al. (2014) "Controlled defects in
semiconducting carbon nanotubes promote efficient generation and
luminescence of trions," ACS Nano 8:4239-4247), thus making them
particularly interesting for emergent photonic applications.
However, these conventional methods for defect creation have thus
far been bound by the extremely limited chemical and optical
tunability. In particular, oxygen doping leads to mixed ether and
epoxide structures, and diazonium chemistry works only for specific
aryl groups and monovalent bonding, and has relatively low reaction
rates. Moreover, it has been demonstrated that diazonium chemistry
and oxidative reactions occur on a SWCNT sidewall at completely
random atomic sites (see Goldsmith et al. (2007)
"Conductance-controlled point functionalization of single-walled
carbon nanotubes," Science 315:77-81); Cognet et al. (2007)
"Stepwise quenching of exciton fluorescence in carbon nanotubes by
single-molecule reactions," Science 316:1465-1468). The covalent
modification of even a single site utilizing such methodologies
results in a substantial drop of electrical conductance (Goldsmith
et al. (2007), Conductance-controlled point functionalization of
single-walled carbon nanotubes," Science 315:77-81) and stepwise
quenching of exciton fluorescence in semiconducting nanotubes
(Cognet et al. (2007), Stepwise quenching of exciton fluorescence
in carbon nanotubes by single-molecule reactions," Science
316:1465-1468). As such, prior methodologies utilizing defects pale
in comparison with the large number of quantum dots that have been
synthesized based on the quantum confinement effect. The use of
defects for materials engineering has therefore not been achieved
by such prior methodologies.
[0008] Accordingly, there is a need for new near-infrared emitters
and synthetic approaches for creating such emitters that overcome
some or all of the difficulties and limitations of conventional
approaches.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a new series of
near-infrared emitters and a versatile new synthetic approach for
creating near-infrared emitters from a single SWCNT material
through molecular engineering of covalently attached surface
functional groups. In accordance with disclosed methodologies, the
synthesis of more than thirty new fluorescent nanostructures is
demonstrated from SWCNTs of the same crystal structure by creating
molecularly tunable fluorescent quantum defects in the sp.sup.3
carbon lattice. Each of the new synthetic nanostructures may be
viewed as a diamond-in-graphene structure reminiscent of an island
in an electron sea.
[0010] In accordance with disclosed embodiments, the present
invention relates to a method of synthesizing a near infrared
emitter comprising the steps of: reacting a carbon nanostructure
with a halogen-containing hydrocarbon precursor and thereby
creating sp.sup.3 defects in said carbon nanostructure, wherein
covalent functionalization produces fluorescent defects that emit
near-infrared radiation having wavelengths between about 800 nm and
about 2500 nm. In some implementations, the sp.sup.3 defects are
created in a pristine carbon nanostructure during said reacting
step.
[0011] In some embodiments, the carbon nanostructure is a carbon
nanotube (CNT), e.g., a single-walled CNT (SWCNT). In some
implementations, the CNT has a diameter of between about 0.5 nm and
about 1.6 nm.
[0012] In some embodiments, the halogen-containing hydrocarbon
precursor is a chlorine, a bromide, an iodide or a di-halide alkyl
precursor. In some embodiments, the halogen-containing hydrocarbon
precursor is a polymer containing the reactive halogen. In some
implementations, the halogen-containing precursor is a
polyoligonucleotide containing the reactive halogen.
[0013] In some embodiments, the halogen-containing hydrocarbon
precursor is an alkyl halide. In some implementations, said
reacting step further comprises combining said carbon nanostructure
with sodium dithionite (Na.sub.2S.sub.2O.sub.4), wherein the sodium
dithionite activates the alkyl precursor.
[0014] In some embodiments, the halogen-containing hydrocarbon
precursor is an iodide or di-halide aryl precursor. In some
implementations, the method provides for exposing the carbon
nanostructure and the aryl precursor to electromagnetic radiation
having a wavelength(s) of between about 300 nm and about 1200 nm,
wherein the wavelength(s) is resonant with the carbon
nanostructures. The electromagnetic radiation activates the aryl
precursor.
[0015] In some embodiments, the created sp.sup.3 defects are
selected from the group consisting of monovalent alkyl defects,
divalent alkyl defects, monovalent aryl defects, and divalent aryl
defects. In some implementations, the covalently functionalized
carbon nanostructure is functionalized with an alkyl group or an
aryl group. In some implementations, the covalently functionalized
carbon nanostructure is functionalized with
--(CH.sub.2).sub.n(CF.sub.2).sub.mCF.sub.3, wherein n is an integer
between 0 and 10, and wherein m is an integer between 0 and 10. In
some implementations, the covalently functionalized carbon
nanostructure is functionalized with --(CH.sub.2).sub.nCH.sub.3,
wherein n is an integer between 0 and 17.
[0016] The present invention also relates to synthesized
near-infrared emitters. In accordance with some embodiments, a
synthetic near-infrared emitter comprises a carbon nanostructure
comprising sp.sup.3 defects in a carbon lattice thereof, which are
created via reaction with a halogen-containing hydrocarbon
precursor. A functional group(s) is covalently bonded to the
sp.sup.3 defects to produce fluorescent defects that emit
near-infrared radiation having wavelengths between about 800 nm and
about 2500 nm.
[0017] In some embodiments, the carbon nanostructure is a carbon
nanotube (CNT), e.g., a SWCNT. In some embodiments, the CNT has a
diameter of between about 0.5 nm and about 1.6 nm.
[0018] In some embodiments, the near-infrared emitter comprises a
functional group is selected from the group consisting of a
monovalent alkyl group, a divalent alkyl group, a monovalent aryl
group, and a divalent aryl group. In some implementations, the
functional group is --(CH.sub.2).sub.n(CF.sub.2).sub.mX, wherein n
is an integer between 0 and 17, and wherein m is an integer between
0 and 17, and wherein X is CH3, CF3, NH2, N+(CH2CH3)2, or COOH. In
some implementations, the functional group is
--(CH.sub.2).sub.nCH.sub.3, wherein n is an integer between 0 and
10.
[0019] The present invention also relates to a quantum emitter
comprising: a semiconductor host; and a fluorescent quantum defect
incorporated into the semiconductor host via optically reacting the
semiconductor host with a molecule comprising a photochemically
activatable moiety that generates a radical that covalently bonds
to the semiconductor host. In preferred embodiments, the quantum
emitter comprises a plurality of fluorescent quantum defects that
are spatially, chemically and/or electronically correlated in the
semiconductor host.
[0020] In some embodiments, the semiconductor host is selected from
the group consisting of a carbon nanotube (CNT), a graphene
nanoribbon, and a carbon nitride. The carbon nanotube may be a
single-walled carbon nanotube (SWCNT) or a double-walled carbon
nanotube (DWCNT). The carbon nanotube may be a SWCNT selected from
the group consisting of a (6,5)-SWCNT, a (10,6)-SWCNT, a
(10,9)-SWCNT, a (10, 3)-SWCNT, a (6,4)-SWCNT, and a
(7,5)-SWCNT.
[0021] In some embodiments, the molecule comprising a
photochemically activatable moiety is a halide-containing molecule.
The halide may iodine, bromine, or chlorine. In some embodiments,
the molecule is an oligonucleotide, e.g., such as a DNA molecule or
an RNA molecule. In preferred embodiments, the oligonucleotide
comprises at least one 5-IododexoyUridine (5I-dU). In some
implementations, the oligonucleotide comprises between 1 and about
1000 nucleotide residues, more preferably between 3 and about 100
nucleotide residues, e.g., between about 5 and about 20 nucleotide
residues. In some embodiments the oligonucleotide comprises a
sequence selected from the group consisting of: 5'-TTA (5I-dU)AT
(5I-dU)AT ATT-3' (SEQ ID NO: 2); 5'-GTT GT(5I-dU) GT(5I-dU) G-3'
(SEQ ID NO: 3); 5'-TT(5I-dU) ATT TA(5I-dU) TTA T-3' (SEQ ID NO: 4);
or 5'-T(5I-dU)A TTA T(5I-dU) A TTG TT-3' (SEQ ID NO: 5).
[0022] The present invention is also directed to a photochemical
method of synthesizing a quantum emitter, comprising the step of:
irradiating a solution comprising a semiconductor host and a
molecule comprising a photochemically activatable moiety, thereby
exciting the semiconductor host and reducing the molecule to
generate a radical, wherein the radical covalently bonds to the
semiconductor host to create a fluorescent quantum defect
thereon.
[0023] In some embodiments, the irradiation step comprises exposing
the solution to radiation having a wavelength of between about 100
nm and about 1400 nm. In some implementations, the solution is
irradiated with visible light. The visible light may have a
wavelength of 565 nm, 765 nm, 892 nm, or 644 nm. In some
implementations, solution is irradiated with radiation having a
wavelength that resonates with an electronic transition(s) of the
semiconductor host. In some implementations, the solution is
irradiated with ultraviolet radiation or near-infrared
radiation.
[0024] In some embodiments, the quantum emitter synthesized in
accordance with disclosed methods comprises a plurality of
fluorescent quantum defects in the semiconductor host. In some
embodiments, the photochemical method comprises the step of
exposing the solution to patterned radiation, thereby creating a
spatially patterned array of fluorescent quantum defects in the
semiconductor host.
[0025] In some embodiments, the molecule comprising a
photochemically activatable moiety utilized in accordance with
disclosed methods comprises at least one halide and aromatic
moieties, and wherein the at least one halide is directly bonded to
at least one of the aromatic moieties. In some implementations, the
at least one halide is iodine, bromine, or chlorine. In some
implementations, the aromatic moieties are benzene, aniline,
nitrobenzene, or benzene sulfonic acid.
[0026] In some implementations, the molecule comprising a
photochemically activatable moiety utilized in accordance with
disclosed methods comprises at least one halide and aromatic
heterocycles, and wherein the at least one halide is bonded to at
least one of the aromatic heterocycles. In some implementations,
the halide is iodine, bromine, or chlorine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The patent or application file contains at least one
drawing/photograph executed in color. Copies of this patent or
patent application publication with color drawing(s) will be
provided by the Office upon request and payment of the necessary
fee.
[0028] FIG. 1 illustrates a fluorescent quantum defect approach to
material engineering as compared to a quantum confinement approach.
Panel a illustrates a quantum confinement system, wherein the
exciton wavefunction is confined as the particle size reaches the
Bohr radius of the quasi-particle, lending the capability to
control optical properties by size engineering. Panel b illustrates
a quantum defect system in accordance with the present invention,
wherein the mobile excitons are trapped and their optical
properties controlled by molecular engineering of the trap. Panel c
illustrates the creation of a fluorescent quantum defect by
reacting a SWCNT semiconductor with an exemplary alkyl iodide
(R-I).
[0029] FIG. 2 illustrates graphically the chemical creation of
fluorescent (6,5)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3. As shown
in Panel a, defect photoluminescence arises farther in the
near-infrared, 190 meV to the red of the parent nanotube excitonic
emission. Correlated visible near-infrared absorption (black line)
and PL (red line) spectra for
(6,5)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 are illustrated
graphically in Panel b, wherein the SWCNTs are excited at the
E.sub.22 transition (565 nm). Evolution of E.sub.11 and
E.sub.11.sub.- emission is illustrated graphically in Panel c.
[0030] FIG. 3 illustrates graphically control reactions with
different reagent conditions (set forth in Table 1). Emission
spectra are monitored with 565 nm excitation at 0 h, 2 h, 24 h, 3
days and 7 days. Only the reaction condition shown in Panel a
exhibits the strong defect PL (En).
[0031] FIG. 4 illustrates graphically that emission energy of
defect photoluminescence is dependent on nanotube diameter.
Chirality enriched carbon nanotubes were used and functionalized
with --CF.sub.2(CF.sub.2).sub.4CF.sub.3 groups.
[0032] FIG. 5 illustrates nanotube structure-dependent defect
photoluminescence. The excitation-emission maps of (6,5)-SWCNT
(Panel a); (8,3)- and (8,4)-SWCNT (Panel b); (7,6)- and
(8,4)-enriched SWCNTs (Panel c); and the mixed chirality of HiPco
SWCNT (Panel d). Controlled sidewall alkylation induces new PL
peaks in (6,5)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 (Panel e);
(8,3)/(8,4)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 (Panel f);
(7,6)/(8,4)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 (Panel g); and
HiPco-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 (Panel h). The
nanotubes were stabilized in D.sub.2O by 1 wt. % sodium dodecyl
sulfate (CH.sub.3(CH.sub.2).sub.11SO.sub.4Na).
[0033] FIG. 6 illustrates graphically emission spectra of
(6,5)-pristine and (6,5)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 and
showing the brightening PL by more than an order of magnitude.
[0034] FIG. 7 illustrates correlated spectral characterization of
functionalized SWCNTs at increasing molar reactant ratios of
CF.sub.3(CF.sub.2).sub.4CF.sub.2I (RX) to the mixed chirality of
HiPco SWCNT carbon, including: Raman scattering (Panel a), wherein
the excitation line is 532 nm; and X-ray photoelectron spectroscopy
(XPS) taken at 25.degree. C. (Panel b), wherein the O1s peak is
marked with an asterisk (*). PL is illustrated graphically in Panel
c. The ratio of covalently attached function group to nanotube
carbon, [R]/[C], as determined from XPS, increases linearly with
the reactant ratio, [RX]/[C], as shown in Panel d. Raman D/G ratio
of SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 at increasing [RX]/[C] is
illustrated in Panel e.
[0035] FIG. 8 illustrates high resolution XPS of C is at
175.degree. C. for SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3. Panel a:
non-functionalized control; Panel b: [C]:[RX]=1:50; Panel c: 1:500;
and Panel d: 1:2500. The nanotubes used were a sample of mixed
chirality HiPco SWCNTs.
[0036] FIG. 9 illustrates high resolution XPS of F is at
175.degree. C. for SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3. Panel a:
Non-functionalized control; Panel b: [C]:[RX]=1:50; Panel c: 1:500;
and Panel d: 1:2500.
[0037] FIG. 10 illustrates high resolution XPS of full spectra at
175.degree. C. for SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3. Panel a:
Non-functionalized control; Panel b: [C]:[RX]=1:50; Panel c: 1:500,
and Panel d: 1:2500.
[0038] FIG. 11 illustrates the spectroscopic characterization of
(6,5)-SWCNT-CH.sub.2(CH.sub.2).sub.4CH.sub.3 stabilized in 1 wt./v
% SDS-D.sub.2O. Defect PL from the chemically tailored (6,5)-SWCNT
is identified in the same emission energy regardless of the source
of raw nanotube materials: two phase separation isolated CoMoCAT
SG65i (Panel a, Panel d and Panel g), gel purified HiPco (Panel b,
Panel e and Panel h), and unpurified CoMoCAT SG65i (Panel c, Panel
f and Panel i). Panel a, Panel b, and Panel c: The
excitation-emission PL map (coded in accordance with key of FIG.
5). Panel d, Panel e, and Panel f: 565 nm single excitation PL
spectra. Panel g, Panel h, and Panel i: UV-vis-NIR absorption
spectra.
[0039] FIG. 12 illustrates the correlated spectral characterization
of functionalized CoMoCAT SWCNTs at an increasing ratio of
--CF.sub.2(CF.sub.2).sub.4CF.sub.3 groups. Panel a: PL; Panel b:
absorption; and Panel c: Raman D/G ratio as a function of [RX]/[C]
molar ratio. Raman spectra with 632.8 nm and 532 nm excitation
laser are illustrated in Panel d and Panel e, respectively.
[0040] FIG. 13 illustrates tunable near-infrared PL from quantum
defect-tailored (6,5)-SWCNTs with six-carbon alkyl chains with an
increasing numbers of fluorine substituents.
[0041] FIG. 14 illustrates correlated UV-Vis-NIR absorption and PL
of (6,5)-SWCNTs with different functional groups.
[0042] FIG. 15 illustrates the emission spectra of (6,5)-SWCNTs
with six carbon alkyl chains before peakfitting. Additional
satellite peaks were observed and marked with asterisk (*) arising
from a charged exciton (trion).
[0043] FIG. 16 illustrates the linear correlation between energy
shift and calculated inductive constant of non-, partially-, and
per-fluorinated alkyl groups. Panel a: Fluorination effects in
hexyl functionalized (6,5)-SWCNTs; Panel b: Effects of chain length
in (6,5)-SWCNT-(CH.sub.2).sub.nCF.sub.3; Panel c: Summary of
inductive effects in the energy shifts.
[0044] FIG. 17 illustrates the energy shift versus calculated
inductive constant with non-, partially-, and per-fluorinated alkyl
groups and tabulates their emission wavelength and energy
shifts.
[0045] FIG. 18 illustrates (6,5)-SWCNT>CF.sub.2. Panel a: PL
maps of pristine SWCNTs (left) and divalent alkyl-functionalized
SWCNTs (right); Panel b: 565 nm excitation emission spectra; Panel
c: UV-Vis-NIR Absorption spectra; Panel d: Raman spectra with 532
nm laser; and Panel e: Raman spectra with 632.8 nm laser. The
pristine is black solid and the functionalized SWCNTs are red solid
line.
[0046] FIG. 19 illustrates the creation of monovalent (Panel a) and
divalent (Panel b) aryl defects of aminobenzene-(6,5)-SWCNTs. The
aryl defect was created by excitation light (300-1200 nm) without
sodium dithionite. Single emission spectra are obtained with 565 nm
excitation light and normalized by E.sub.11.
[0047] FIG. 20 illustrates a comparison of monovalent and divalent
fluorescent quantum defects. The nanotubes were excited at 565 nm.
The parent exciton PL occurs at 979 nm while emission from the
quantum defects are systematically tunable by changing the
functional group including --CH.sub.3, >CH.sub.2,
--C.sub.6H.sub.5, and >C.sub.6H.sub.4. The spectra are fitted
with Voigt functions.
[0048] FIG. 21 illustrates excitation-emission maps of (6,5)-SWCNTs
with chemically tailored fluorescent quantum defects.
[0049] FIG. 22 illustrates schematically four classes of quantum
defects.
[0050] FIG. 23 illustrates pH-responsive defect photoluminescence
of monovalent (Panel a) and divalent (Panel b)
aminobenzene-functionalized (6,5)-SWCNTs.
[0051] FIG. 24 illustrates fluorescent aryl defects in
semiconducting SWCNTs. Panel a: Schematic representation of light
activated arylation in a (6,5)-SWCNT. Absorption of light by the
SWCNT generates a hot electron, which subsequently transfers to a
4-iodoaniline molecule, yielding an aryl radical that can bond to
the carbon nanotube surface. Panel b: UV-vis-NIR absorption spectra
of 4-iodoaniline (dotted line) and the pristine (6,5)-SWCNTs (solid
line) in 1% sodium dodecyl sulfate-D.sub.2O shows that the nanotube
can be excited to the exclusion of 4-iodoaniline at the E.sub.22
van Hove transition (.about.565 nm). The photoluminescence spectrum
(gray line) of (6,5)-SWCNTs with aryl quantum defects features a
redshifted emission, E.sub.11.sub.-.
[0052] FIG. 25 illustrates PL emission spectra of (6,5)-SWCNTs
during the first 10 min of the continuous irradiation at 565 nm (at
minutes 0, 2, 4, 6, 8 and 10).
[0053] FIG. 26 illustrates the photochemical nature of the light
activated reaction. Panel a: The excitation-emission PL maps of the
pristine (6,5)-SWCNTs (top), (6,5)-SWCNTs that exposed to
4-iodoaniline under dark, thermal (70.degree. C. for 1 h) (middle),
and photochemical (565 nm excitation for 10 min) (bottom)
conditions. The PL spectra of the (6,5)-SWCNT suspension before and
after it was exposed to 4-iodoaniline mixture and the solution was
then (Panel b) protected from light and the temperature was
elevated to 70.degree. C. for 1 h, or (Panel c) under 10 min of
continuous irradiation at 565 nm.
[0054] FIG. 27 illustrates Raman spectra of (6,5)-SWCNTs. Panel a:
Raman spectra of (6,5)-SWCNTs plus 4-iodoaniline after 30 min and
10 min irradiation at 565 nm (black and red) and the pristine
control (green). The intensity is normalized to the G band. Raman
spectra were collected with 532 nm excitation in duo scan mode that
averages spectra from a 20.times.20 .mu.m.sup.2 area. Panel b:
Enlarged Raman spectra of the radial breathing mode (RBM) and D
band. Panel c: The integrated intensity ratio of the D band
(1250-1350 cm.sup.-1) to G band (1475-1650 cm.sup.-1). The D/G
ratio increased from 0.016 to 0.040 after 30 min irradiation in the
presence of 4-iodoaniline. Error bars are standard deviations of
the D/G ratio values for 10 Raman scans.
[0055] FIG. 28 illustrate PL spectra before and after irradiation,
showing (Panel a) 10 min irradiation of (6,5)-SWCNT solution alone,
or (Panel b) by adding just sodium bicarbonate and no 4-iodoaniline
to the solution does not create new PL emission. The small PL peak
at 1115 nm originates from the phonon sideband of the E.sub.11
excitons.
[0056] FIG. 29 illustrates that kinetics of the photochemical
arylation of (6,5)-SWCNT with 4-iodoaniline. Panel a: Evolution of
the E.sub.11 and E.sub.11.sub.- emissions. The intensity of the
E.sub.11.sub.- emission reached a maximum after 13 min of
continuous irradiation with 565 nm light while the E.sub.11
emission continued to decrease. Panel b: The relation between
I.sub.0/I.sub.11.sub.- and the reaction time (dots) was used to
extract the light-activated reaction rate by fitting the data with
eq. 7 (line).
[0057] FIG. 30 illustrates the use of light to drive the reaction.
Panel a: The photoluminescence spectra of the (6,5)-SWCNT and
4-iodoaniline mixture after it was protected from light and the
temperature was elevated to 70.degree. C. for 3 h and then
subsequently exposed to 565 nm light for 10-30 min. Panel b: The
evolution of the integrated E.sub.11.sub.-1/E.sub.11 area ratio
(I.sub.11.sub.-/I.sub.11) over time during the heating and
subsequent irradiation periods. No reaction occurred during the
heating phase as evidenced by the absence of defect PL. The defect
PL, however, immediately evolved upon 565 nm light irradiation.
[0058] FIG. 31 illustrates the light-induced electron transfer
driving the reaction. Panel a: The degree of functionalization
estimated by I.sub.11.sub.-/I.sub.11 (circles) closely follows the
(6,5)-SWCNT absorption spectrum (black line trace). High reaction
efficiencies were observed when the wavelength of the irradiating
light resonated with the electronic transitions (E.sub.22 and
E.sub.33) of the (6,5)-SWCNTs. Panel b: The reaction rate (k.sub.c)
demonstrates a linear relationship (R.sup.2=0.999) with the
irradiation power. Panel c: The electronic structures of
(6,5)-SWCNTs and iodobenzene depict the electron transfer mechanism
from the valence band of the (6,5)-SWCNT to the LUMO of
iodobenzene.
[0059] FIG. 32 illustrates the irradiation power affecting the
degree of functionalization. The evolution of the
I.sub.11.sub.-/I.sub.11 ratio over time at various photon fluences
of 565 nm light. Regardless of the photon fluence, the evolution of
the PL intensity was highly linear with the irradiation time
(R.sup.2=0.999).
[0060] FIG. 33 illustrates the density functional theory (DFT)
calculations showing the lowest unoccupied molecular orbital (LUMO)
for physisorbed iodobenzene on a 10 nm (6,5)-SWCNT. Panel a: The
density of states versus energy plot of 10 nm long (6,5)-SWCNT and
the LUMO of physisorbed iodobenzene. The .pi.-.pi. stacking between
iodobenzene and SWCNT lowers the LUMO of iodobenzene. Panel b: LUMO
of physisorbed iodobenzene that exhibits the electronic coupling
with LUMO+29 of (6,5)-SWCNT. Isocontour is 0.002.
[0061] FIG. 34 illustrates the PL spectra of (6,5)-SWCNTs
functionalized by different aryl halides (C.sub.6H.sub.5X,
X.dbd.Cl, Br, or I) under 20 min irradiation of 565 nm light at 7.5
mW. Each PL spectra is normalized to the En PL. Fluorescent quantum
defects can be created by irradiation from virtually any aryl
halide precursor except aryl fluoride.
[0062] FIG. 35 illustrates the molecularly tunable emission energy
of the defect PL. The new defect photoluminescence can be
controlled by changing the terminating groups of the aryl halide.
The energy difference between E.sub.11 and E.sub.11.sub.-
(.DELTA.E.sub.optical) is linearly correlated to the electron
withdrawing ability of the moieties, which can be quantified with
the Hammett constant.
[0063] FIG. 36 illustrates precisely controlled synthesis of
quantum defects using light in accordance with disclosed methods.
The circle data points display the I.sub.11.sub.-/I.sub.11 ratio
for a mixture of (6,5)-SWCNTs and 4-iodoaniline that was irradiated
for 2 min at 565 nm (ON) and then left for 3 min without
irradiation (OFF) in an alternating fashion. The square data points
correspond to the thermal control.
[0064] FIG. 37 illustrates the absorption (Panel a) and
photoluminescence (Panel b) spectra of the DNA dispersed (6,5)
enriched SWCNTs solution.
[0065] FIG. 38 illustrates schematically the light-triggered
photochemical reaction for creating a quantum defect pattern in a
single tube using a modified DNA sequence (Panel a). The excitation
and emission map of the DNA dispersed (6,5) SWNT enriched solution
before (Panel b) and after (Panel c) exposure to 565 nm light.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0066] The present invention relates to a new series of
near-infrared emitters and a versatile new synthetic approach for
creating near-infrared emitters from a single carbon nanostructure
material, e.g., SWCNT, through molecular engineering of covalently
attached surface functional groups (FIG. 1). Utilizing the
disclosed methodologies, the synthesis of more than thirty new
exemplary fluorescent nanostructures was achieved from SWCNTs of
the same crystal structure by creating molecularly tunable
fluorescent quantum defects in the sp.sup.3 carbon lattice. Each of
the new synthetic nanostructures may be viewed as a
diamond-in-graphene structure reminiscent of an island in an
electron sea.
[0067] The present invention also relates to a class of quantum
emitters, each of which contains a plurality of fluorescent defect
sites that are incorporated into a semiconductor host with spatial,
chemical and/or electronical correlations. Also disclosed are
methods of synthesizing these light-emitting polymers by
incorporating halide moieties within their structure and reacting
them with carbon nanotube semiconductor hosts.
[0068] Fluorescent quantum defects are a new class of synthetic
single-photon emitters with vast potential, e.g., for near-infrared
imaging, chemical sensing, materials engineering, and quantum
information processing. Such emitters can be synthetically created
in solid-state hosts, such as semiconducting single-walled carbon
nanotubes (SWCNTs), by covalently attaching organic functional
groups (Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem 5(10):840-845; Kwon, H. et al. (2016) "Molecularly Tunable
Fluorescent Quantum Defects," J. Am. Chem. Soc. 138:6878-6885).
These quantum defects produce localized potential wells that can
efficiently capture mobile excitons and enable them to recombine
radiatively (Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem 5(10):840-845). It has recently been demonstrated that quantum
defect emission energies are molecularly tunable depending on the
chemical nature and bonding configuration of the covalently
attached group (Kwon, H. et al. (2016) "Molecularly Tunable
Fluorescent Quantum Defects," J. Am. Chem. Soc. 138:6878-6885; Ma,
X. et al. (2014) "Electronic structure and chemical nature of
oxygen dopant states in carbon nanotubes," ACS Nano 8:10782-10789;
He, X. et al. (2017) "Low-Temperature Single Carbon Nanotube
Spectroscopy of sp3 Quantum Defects." ACS Nano
10.1021/acsnano.7b03022).
[0069] As demonstrated herein, the synthetic creation of
molecularly tunable fluorescent quantum defects in semiconducting
single-walled carbon nanotube hosts may be optically directed via
photochemical reactions. By exciting the host semiconductor with
light that resonates with its electronic transition,
halide-containing aryl groups covalently bond to the sp.sup.2
carbon lattice. The introduced quantum defects generate bright
photoluminescence that allows tracking of the reaction progress in
situ. The reaction is independent of temperature but correlates
strongly with the photon energy used to drive the reaction,
indicating a photochemical mechanism rather than photo-thermal
effects. The disclosed photochemical reactions provide for control
of the synthesis of fluorescent quantum defects using light, and
enable lithographic patterning of quantum emitters with electronic
and molecular precision.
[0070] Beyond presenting a new class of tunable quantum light
sources, these synthetic defects can also brighten dark excitons
(Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem 5(10):840-845), facilitate upconversion (Akizuki, N. et al.
(2015) "Efficient near-infrared up-conversion photoluminescence in
carbon nanotubes," Nat. Commun. 6:8920), stabilize trions (Brozena,
A. H. et al. (2014) "Controlled defects in semiconducting carbon
nanotubes promote efficient generation and luminescence of trions,"
ACS Nano 8:4239-4247), and produce high purity single photons at
telecomm wavelengths at room temperature (He, X. et al. (2017)
"Tunable room-temperature single photon emission at telecom
wavelengths from sp3 defects in carbon nanotubes," Nat. Photonics
11:577-582). Fluorescent quantum defects therefore hold vast
potential for near-infrared (IR) imaging (Hong, G. et al. (2015)
"Carbon Nanomaterials for Biological Imaging and Nanomedicinal
Therapy," Chem. Rev. 115(19):10816-10906), optical sensing (Kwon,
H. et al. (2015) "Optical Probing of Local pH and Temperature in
Complex Fluids with Covalently Functionalized, Semiconducting
Carbon Nanotubes," J. Phys. Chem. 119(7):3733-3739; Shiraki, T. et
al. (2016) "Near infrared photoluminescence modulation of
single-walled carbon nanotubes based on a molecular recognition
approach," Chem. Commun. (Camb.) 52(88):12972-12975), and quantum
information processing (Aharonovich, I. et al. (2016) "Solid-state
single photon emitters," Nat. Photonics 10:631-641).
[0071] Developing ways to controllably introduce or pattern
fluorescent quantum defects is thus important for such
applications. Recent experiments have demonstrated that optical
excitation of SWCNTs can induce local heating (Powell, L. R. et al.
(2016) "Optical Excitation of Carbon Nanotubes Drives Localized
Diazonium Reactions," J. Phys. Chem. Lett. 15(7):3690-3694; Chiu,
C. F. et al. (2017) "Defect-Induced Near-Infrared Photoluminescence
of Single-Walled Carbon Nanotubes Treated with Polyunsaturated
Fatty Acids," J. Am. Chem. Soc. 139:4859; Wang, C. et al. (2017)
"Optically Triggered Melting of DNA on Individual Semiconducting
Carbon Nanotubes," Angew. Chem. Int. Ed. Engl. 56(32):9326-9330;
Powell, L. R. et al. (2017) "Chirality-Selective Functionalization
of Semiconducting Carbon Nanotubes with a Reactivity-Switchable
Molecule," J. Am. Chem. Soc. 139(36):12533-12540; Ng. A. L. et al.
(2017) "Laser Lithography of a Tube-in-a-Tube Nanostructure," ASC
Nano. 11(3):3320-3327). This photothermal effect can significantly
accelerate chemical reactions (Powell, L. R. et al. (2016) "Optical
Excitation of Carbon Nanotubes Drives Localized Diazonium
Reactions," J. Phys. Chem. Lett. 15(7):3690-3694), de-functionalize
surface functional groups (Ng. A. L. et al. (2017) "Laser
Lithography of a Tube-in-a-Tube Nanostructure," ASC Nano.
11(3):3320-3327) and makes it possible to selectively react a
specific nanotube within a mixture (Powell, L. R. et al. (2017)
"Chirality-Selective Functionalization of Semiconducting Carbon
Nanotubes with a Reactivity-Switchable Molecule," J. Am. Chem. Soc.
139(36):12533-12540). However, because it is difficult to spatially
confine the thermal effect, it is challenging to use this thermal
effect for precise control of the reaction site at the molecular
level.
[0072] In accordance with disclosed embodiments, a photochemical
reaction is provided for creating molecularly tunable fluorescent
quantum defects in semiconducting hosts (e.g., SWCNTs) with
electronic controls. As demonstrated herein, reactions between an
aryl halide and the nanotube can be triggered photochemically. The
semiconducting nanotube is optically excited, reducing the aryl
halide to a radical that covalently bonds to the nanotube host to
create the fluorescent quantum defect (FIG. 24, Panel a). This
photochemical reaction is nearly independent of solution
temperature, but correlates strongly with the photon energy and
fluence used to drive the reaction.
[0073] As used herein, the term "carbon nanostructure" refers to
allotropic forms of carbon, with or without impurities, in the form
of a single-walled or multi-walled tube, cylinder, sphere, crystal,
sheet, rod, or other structure. In some embodiments, the carbon
nanostructure is a carbon nanotube (CNT) having a generally
cylindrical nanostructure. CNTs may be differentiated according to
their chirality, diameter, wall number, and/or electrical
properties. In some implementations, the CNT is a single-walled CNT
(SWCNT). In other implementations, the CNT is a multi- or
double-walled CNT (e.g., DWCNT). In some implementations, the CNT
is a small diameter CNT (e.g., having a diameter of less than about
1 nm, or less than about 0.5 nm). In other implementations, that
CNT is a large diameter CNT (e.g., having a diameter of more than
about 1 nm, or more than about 2.0 nm). In some implementations,
the CNT has a diameter of between about 0.5 nm and about 1.6 nm. A
"covalently functionalized CNT" refers to a CNT having a surface
functional group(s) attached to the carbon sidewall or lattice via
a covalent bond.
[0074] The term "pristine carbon nanostructure" refers to a carbon
nanostructure, e.g., a CNT, that has no observable surface
modifications (except, e.g., at the nanotube ends of a CNT, as
determined by Raman spectroscopy or other methods known in the
art).
[0075] The term "substantially pure CNT" as used herein refers to a
CNT or covalently functionalized CNT comprising more than about 80%
of one type, and/or chirality and less than about 20% of other
types and/or chiralities as established using conventional
analytical methods, e.g., UV-vis-Near Infrared Spectroscopy,
routinely used by those of skill in the art. In one embodiment, the
amount of other types and/or chiralities in a substantially pure
CNT or covalently functionalized CNT is less than about 20%, less
than about 10%, less than about 5%, less than about 2%, less than
about 1%, or less than about 0.5%.
[0076] The term "defect" as used herein refers to an irregularity
in the bonding network or lattice of a carbon nanostructure. In
some embodiments, the defect is a sp.sup.3 defect.
[0077] The term "alkylating agent" as used herein refers to reagent
capable of placing an alkyl group onto a nucleophilic site,
including, but not limited to, organic halides.
[0078] In the case of semiconducting nanotubes with fluorescent
defects, such structures can be viewed as hybrid quantum systems
that allow excitation energy (carried by the exciton) to be
channeled along a one-dimensional (1D) antenna and then harvested
using a zero-dimensional (OD) funnel. Compared with quantum
confinement, which controls the optical and electronic gap by size
engineering, the fluorescent defects in SWCNTs create local
potential wells that can be chemically tailored with superior
molecular-control as shown herein. To recognize their molecular
nature and the fact that the local potential well is a result of
defect-induced splitting of frontier orbitals, the defects may be
referred to herein as fluorescent quantum defects. Furthermore,
unlike atomic color-center dopants, the defect-inducing surface
functional groups are themselves non-emitting and readily
accessible chemically, thereby affording unprecedented molecular
control and engineering flexibility as compared to prior
methodologies.
[0079] In accordance with disclosed embodiments, the molecularly
tunable fluorescent quantum defects are achieved by a versatile new
chemistry that allows covalent attachment of bromine or
iodine-containing hydrocarbon precursors to the sp.sup.2 carbon
lattice through highly predictable C--C bonding. The reaction
occurs in aqueous solution upon mixing an alkyl halide with
nanotubes in the presence of sodium dithionite
(Na.sub.2S.sub.2O.sub.4) which acts as a mild reductant (see Zhang,
C.-P. et al. (2012) "Progress in fluoroalkylation of organic
compounds via sulfinatodehalogenation initiation system," Chem.
Soc. Rev. 41:4536-4559). We note that sidewall alkylation can occur
under extreme conditions, such as in the Billups-Birch reaction in
which solvated electrons in liquid ammonia are required (Liang, F.
et al. (2004) "Convenient Route to Functionalized Carbon
Nanotubes," Nano Lett. 4:1257-1260; Deng, S. et al. (2011)
"Confined propagation of covalent chemical reactions on
single-walled carbon nanotubes," Nat. Commun. 2). In contrast, the
disclosed methodologies are significantly more versatile because
molecularly tunable fluorescent quantum defects can be created with
highly predictable C--C bonding points from virtually any
iodine-containing hydrocarbon precursor. Notably, this
exciton-tailoring chemistry is not limited to the creation of
monovalent alkyl defects. Rather, both monovalent and divalent
defects can be created by reacting SWCNTs with respective iodide or
di-iodide alkyl or aryl precursors. In contrast to alkyl iodides,
which provide for activation by sodium dithionite, aryl iodides
alone can react with SWCNTs by resonantly exciting the nanotubes
with visible light. Furthermore, the aqueous medium allows for in
situ probing of the evolution of sidewall alkylation and provides a
level of control that was previously unattainable (Ghosh, S. et al.
(2010) "Oxygen doping modifies near-infrared band gaps in
fluorescent single-walled carbon nanotubes," Science 330:1656-1659;
Piao, Y. M. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem. 5:840-845).
[0080] In accordance with one embodiment, a new exciton-tailoring
reaction is provided, which occurs in aqueous solution upon mixing
an alkyl halide with nanotubes in the presence of the mild
reductant sodium dithionite (FIG. 3 and Table 1). Alkyl halides
alone cannot generate alkyl radicals that covalently attach to the
carbon lattice (FIG. 3, Panel c and Panel i). Control experiments
indicated that the reaction is facilitated by acetonitrile, which
acts as a co-solvent for the alkyl halides, not required to
generate defect photoluminescence (FIG. 3, Panel b and Panel f).
Sodium bicarbonate serves as a base to balance acidic byproducts of
sodium dithionite (FIG. 3, Panel d and Panel h) as explained with
organic small molecules (Zhang, C.-P. et al. (2012) "Progress in
fluoroalkylation of organic compounds via sulfinatodehalogenation
initiation system," Chem. Soc. Rev. 41:4536-4559; Xiao, Z. et al.
(2013) "Radical Addition of Perfluoroalkyl Iodides to Alkenes and
Alkynes Initiated by Sodium Dithionite in an Aqueous Solution in
the Presence of a Novel Fluorosurfactant," Chin. J. Chem.
31:939-944).
TABLE-US-00001 TABLE 1 Control reactions with different reagent
conditions Reaction SWCNT CH.sub.3CN C.sub.6F.sub.13I NaHCO.sub.3
Na.sub.2S.sub.2O.sub.4 E.sub.11.sub.- a 1 0.2 10 20 10 strong b 1
0.2 -- -- -- -- c 1 -- 10 -- -- -- d 1 -- -- 20 -- -- e 1 -- -- --
10 -- f 1 -- 10 20 10 weak g 1 0.2 -- 20 10 -- h 1 0.2 10 -- 10 --
i 1 0.2 10 20 -- --
[0081] The emission energy of the alkylated carbon nanotubes showed
a strong dependence on nanotube diameter, d, by
.DELTA.E=A/d.sup.2+B with A=-126.8 meV nm.sup.2 and B=18.1 meV,
suggesting that the new emission peak arises from brightening of
dark excitons (FIGS. 4 and 5) (Piao, Y. et al. (2013) "Brightening
of carbon nanotube photoluminescence through the incorporation of
sp3 defects," Nat. Chem. 5:840-845; Capaz, R. B. et al. (2006)
"Diameter and chirality dependence of exciton properties in carbon
nanotubes," Phys. Rev. B 74, 121401). Notably, the
(6,5)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 exhibits PL that is
brighter than that of the parent nanotube by more than an order of
magnitude (FIG. 6).
[0082] Correlated measurement of PL, Raman scattering, and X-ray
photoelectron spectroscopy (XPS) unambiguously confirmed that the
new PL originates from sp.sup.3 quantum defects due to the covalent
attachment of a small number of the alkyl groups to the sp.sup.2
carbon lattice (FIG. 7). The formation of a covalent C--C bond
between the alkyl group and the carbon nanotube is evidenced by the
rise of the symmetry-breaking, defect-induced Raman scattering of
the D phonon (.about.1,300 cm.sup.-1) (Dresselhaus, M. S. et al.
(2007) "Raman Spectroscopy of Carbon Nanotubes in 1997 and 2007,"
J. Phys. Chem. C 111:17887-17893). The intensity of this Raman band
with respect to the in-plane stretching mode (E.sub.2g) of the
sp.sup.2 bonded carbon lattice (G band, .about.1590 cm.sup.-1)
increased from 0.10 to 0.98 in highly functionalized nanotubes
(FIG. 7, Panel a). Both the Raman D/G ratio and the XPS intensity
of the perfluoroalkyl group increased in proportion to the relative
concentration of alkyl halide (FIG. 7, Panels a and b, and FIG. 9).
High resolution XPS of SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 shows
the growth of the sp.sup.3 C1s peak at 285 eV as a shoulder to the
sp.sup.2 C1s peak (284.7 eV), resulting in substantial peak
broadening of the C1s peak (FWHM of 1.46 eV versus 0.83 eV for the
starting nanotubes) (FIG. 8). The fluorine (F1s) signal of the
functional group remained constant at high temperature (e.g.,
175.degree. C.) in ultrahigh vacuum (<1.times.10.sup.-8 torr),
in which there are no physisorbed molecules (FIG. 10).
[0083] The new defect PL was further investigated with different
SWCNT samples such as HiPco ensemble, CoMoCAT ensemble, the aqueous
two phase-assisted SWCNTs (Ao, G. et al. (2014) "DNA-Controlled
Partition of Carbon Nanotubes in Polymer Aqueous Two-Phase
Systems," J. Am. Chem. Soc. 136:10383-10392) and the
column-purified SWCNTs to rule out the possibility of impurity
effects (see FIG. 11). FIG. 11 illustrates the spectroscopic
characterization of (6,5)-SWCNT-CH.sub.2(CH.sub.2).sub.4CH.sub.3
stabilized in 1 wt./v % SDS-D.sub.2O. Defect PL from the chemically
tailored (6,5)-SWCNT can be clearly identified in the same emission
energy regardless of the source of raw nanotube materials: two
phase separation isolated CoMoCAT SG65i (FIG. 11, Panels a, d and
g), gel purified HiPco (FIG. 11, Panels b, e, and h), and
unpurified CoMoCAT SG65i (FIG. 11, Panels c, f and i). FIG. 11,
Panels a, b and c: The excitation-emission PL map. FIG. 11, Panels
d, e and f: 565 nm single excitation PL spectra (E.sub.11 and
E.sub.11.sub.- PL positions marked). FIG. 11, Panels g, h and i:
UV-vis-NIR absorption spectra. These results demonstrate the defect
PL is unique with new properties incorporated through the chemical
modification. All showed the consistent .DELTA.E of defect PL for
the (6,5) chirality tubes for all tested samples. Furthermore, the
correlated emission, absorption and Raman with
(6,5)-CoMoCAT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 showed identical
results of close relationship between covalent attachment and
defect PL brightening (FIG. 12).
[0084] By changing the concentrations of the reagents, the
intensity of the defect PL was controlled. The E.sub.11.sub.-
intensity of (6,5)-SWCNT-CF.sub.2(CF.sub.2).sub.4CF.sub.3 peaks at
a carbon-to-alkyl halide reactant molar ratio of 1 to 0.4 (FIG. 2).
Correspondingly, the Raman D/G ratio increased from 0.10 to 0.18,
indicating that a small amount of alkyl groups were covalently
attached on the nanotubes. Consistent with Raman scattering, the
visible near-infrared absorption barely decreased. Based on XPS
(FIGS. 2 and 7), the attached --CF.sub.2(CF.sub.2).sub.4CF.sub.3
groups were estimated to be at a density of one group per 166
carbons or 1.8 nm of nanotube length on average. This density is
much higher than that produced by diazonium salts (see Piao, Y. et
al. (2013) "Brightening of carbon nanotube photoluminescence
through the incorporation of sp3 defects," Nat. Chem. 5:840-845)
and may suggest distinct reaction propagation (Zhang, Y. et al.
(2013) "Propagative Sidewall Alkylcarboxylation that Induces
Red-Shifted Near-IR Photoluminescence in Single-Walled Carbon
Nanotubes," J. Phys. Chem. Lett. 4:826-830).
[0085] Tunable Fluorescent Quantum Defects with Alkylation
[0086] The disclosed synthetic quantum systems provide exceptional
chemical tunability of the near-infrared PL energy (FIGS. 13 and
15). Continuous red-shift of the E.sub.11.sub.- emission was
achieved simply by increasing the number of fluorine atoms along a
six-carbon alkyl backbone (FIG. 13 Panel b, and FIG. 16 Panel a,
and Table 2). The energy shift moved from 133 meV for
--CH.sub.2(CH.sub.2).sub.4CH.sub.3 to 190 meV for
--CF.sub.2(CF.sub.2).sub.4CF.sub.3. A consistent trend was observed
in a series of partially fluorinated groups in which the distance
between the electron withdrawing moiety (--CF.sub.3) and the defect
site was varied by the chain length, --(CH.sub.2).sub.nCF.sub.3
(n=0-5), (see FIG. 16 Panel b, and Table 2), resulting in the
energy shift from 137 meV to 194 meV. When the first carbon of
alkyl chains that is directly attached to a SWCNT was fluorinated,
it significantly affected the energy separation, indicating strong
distance effect.
TABLE-US-00002 TABLE 2 Spectral characteristics of alkyl
fluorescent quantum defects in (6,5) SWCNTs and calculated
inductive constants of the covalently bonded alkyl groups. E.sub.11
E.sub.11.sub.- E.sub.11 FWHM E.sub.11.sub.- FWHM .DELTA. E .sigma.*
(6,5)-SWCNT-R (nm) (meV) (nm) (meV) (meV) (calc) Non-functionalized
979 37 -- -- 0 --
--CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.3 981 45 1096 56
133 -0.774 --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.3 980
45 1099 56 137 -0.462
--CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.2CF.sub.3 980 38 1107 59
146 -0.127 --CH.sub.2CH.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.3 983
40 1137 76 170 1.086
--CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.3 981 42 1155 69
190 4.867 --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.3 980 45
1099 56 137 -0.462 --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.3 979
40 1104 59 143 -0.287 --CH.sub.2CH.sub.2CH.sub.2CF.sub.3 980 42
1101 55 140 -0.034 --CH.sub.2CH.sub.2CF.sub.3 980 42 1110 59 147
0.310 --CH.sub.2CF.sub.3 982 42 1114 67 150 1.244 --CF.sub.3 980 45
1158 63 194 3.961
[0087] The optical properties of tunable fluorescent quantum
defects with alkyl groups are strikingly different from those of
nanocrystals. The size engineering of nanoparticles results in
significant change in band gaps and thus both absorption and
emission are size-dependent. However, the disclosed alkylation
method on the same size nanotube at low defect density can modulate
emissions that are created at defect center while retaining similar
absorption characteristics through chemical engineering of the
surface (FIG. 14). Using this technique, the absorption of
functionalized SWCNTs are comparable with that of pristine SWCNTs
while their emissions can be efficiently tuned by changing
functionality.
[0088] Inductive Effects of Alkyl Defects
[0089] Experimental results and quantum chemical theory
consistently indicated that this tunability originates from
inductive electronic effects associated with the covalently
attached functional group (FIG. 16). These inductive electronic
effects can be described by the empirical Taft constant or
inductive constant (.sigma.*), which quantifies the electronic
influence of a substituent through sigma bonding in alkyl chains,
excluding resonance effects that also occur in conjugated moieties
(Artem, R. C. et al. (1996) "The problem of the quantitative
evaluation of the inductive effect: correlation analysis," Russ.
Chem. Rev. 65:641; Hansch, C. et al. (1991) "A survey of Hammett
substituent constants and resonance and field parameters," Chem.
Rev. 91:165-195). Consistent with this inductive picture, all
perfluorinated alkyl defects in (6,5)-SWCNTs, including --CF.sub.3,
--(CF.sub.2).sub.3CF.sub.3, --(CF.sub.2).sub.5CF.sub.3, and
--(CF.sub.2).sub.7CF.sub.3, produced similarly redshifted
E.sub.11.sub.- peaks (by 190-194 meV), indicating comparable
inductive constants regardless of the carbon chain length (FIG.
17). For CF.sub.3-terminated alkyl defects, the defect PL energy
decreased exponentially with chain length (or approximately, the
distance from the defect site) (Table 2).
[0090] Quantitatively, the inductive constants can be calculated
from the following equation proposed by Cherkasov et al. (see
Artem, R. C. et al. (1996) "The problem of the quantitative
evaluation of the inductive effect: correlation analysis," Russ.
Chem. Rev. 65:641):
.sigma.*=7.840.SIGMA..sub.i.DELTA..chi..sub.iR.sub.i.sup.2/r.sub.i.sup.2
where .DELTA..chi..sub.i is the difference between the
electronegativities of i-th atom in the substituent and the
reaction center, R.sub.i is the covalent radius of the i-th atom,
and r.sub.i is the distance from this atom to the defect site on a
SWCNT. The PL energy shifts are linearly correlated with the
calculated inductive constants (.sigma.*.sub.calc) (FIG. 16). This
linear correlation confirms that the inductive effects associated
with the alkyl groups on the fluorescent quantum defects are
responsible for the observed energy shifts. It is noted that more
than twenty different types of scales exist for inductive constants
reported, which all correlate well with one another. It was found
that reported inductive constants from literature for alkyl groups
used matched with the calculated results herein.
[0091] Creation of Extended Fluorescent Quantum Defects: Aryl and
Divalent Defects
[0092] The disclosed methodologies of creating fluorescent quantum
defects are not limited to creating monovalent alkyl defects (--R),
but also extend to divalent alkyl defects (>R) with di-iodide
precursors (FIG. 18). The diiodo reactions do not typically occur
in organic molecular systems (Zhang, C.-P. et al. (2012) "Progress
in fluoroalkylation of organic compounds via
sulfinatodehalogenation initiation system," Chem. Soc. Rev.
41:4536-4559), while only few conjugated structures with highly
substituted .pi.-bonds are reported to yield carbene-like products
(Kropp, P. J. (1984) "Photobehavior of alkyl halides in solution:
radical, carbocation, and carbene intermediates," Acc. Chem. Res.
17:131-137). Divalent alkyl defects are characterized by PL,
UV-Vis-NIR absorption and Raman spectra showing distinct different
optical properties from monovalent defects including further
redshifted defect PL at 1164 nm.
[0093] In contrast to alkyl iodides, which provide for activation
by sodium dithionite, aryl iodides alone can react with SWCNTs by
electromagnetic radiation or excitation light activation (FIG. 19).
The wavelength(s) of the electromagnetic radiation is resonant with
the SWCNTs for activation. By shining excitation light, e.g.,
having a wavelength(s) from 300 nm to 1200 nm with 5 nm increment,
the wavelength resonant with the SWCNTs, we observed the
development of defect photoluminescence with 159 meV energy shift
for mono-aminobenzene defect and 171 meV shift for divalent
aminobenzene defects starting from with 4-iodoaniline and
3,4-diidoaniline, respectively. It is believed that high .pi.-.pi.
interaction between aryl groups and carbon nanotubes leads to
physisorption of aryl groups as a first step, followed by creating
aryl radicals with incident light to form a covalent bond. Once the
first iodide on the benzene ring reacts, there is a high
possibility that the second iodide at ortho-positions will interact
with SWCNTs, leading to subsequent reactions on an adjacent carbon
of the defect center on the rigid SWCNT structures.
[0094] Tunable Fluorescent Quantum Defects Through Aryl and
Divalent Groups
[0095] Larger optical tunability can be achieved by applying
diiodo-containing precursors to produce cycloaddition adducts. The
divalent quantum defects fluoresce even further into the infrared
than do the monovalent defects (FIG. 20). For instance, PL of
(6,5)-SWCNT>CH.sub.2 occurred at 1125 nm, which was red-shifted
by 31 meV more than its monovalent counterpart,
(6,5)-SWCNT-CH.sub.3. In (6,5)-SWCNT>CF.sub.2, the defect PL was
further shifted to 1164 nm, 200 meV to the red of the parent
nanotube PL. Divalent aryl defects, created by reaction with
o-diiodoaniline and o-diiodobenzene for instance, also produced new
PL peaks that redshifted farther from the parent nanotube, in
comparison with their monovalent counterparts, by 171 meV and 190
meV, respectively (FIG. 20 and Table 3).
TABLE-US-00003 TABLE 3 PL spectral characteristics of (6,5)-SWCNTs
covalently functionalized with different monovalent and divalent
groups. monovalent divalent E.sub.11 E.sub.11- .DELTA. E E.sub.11
E.sub.11- .DELTA. E (6,5)-SWCNT-R (nm) (nm) (meV) (6,5)-SWCNT-R
(nm) (nm) (meV) --CH.sub.3 ##STR00001## 980 1094 132 >CH.sub.2
##STR00002## 980 1125 163 --CF.sub.3 ##STR00003## 980 1158 194
>CF.sub.2 ##STR00004## 980 1164 200 --C.sub.6H.sub.5
##STR00005## 979 1129 168 >C.sub.6H.sub.4 ##STR00006## 986 1162
190 --C.sub.6H.sub.4NH.sub.2 ##STR00007## 980 1121 159
>C.sub.6H.sub.3NH.sub.2 ##STR00008## 980 1133 171
[0096] This novel chemistry allows molecularly tunable fluorescent
quantum defects to be created with highly predictable C--C bonding
points from a halogen-containing hydrocarbon precursor, including
monovalent and divalent alkyl defects and monovalent and divalent
aryl defects (FIGS. 21 and 22). In preferred embodiments, the
halogen-containing hydrocarbon precursor is a chlorine, a bromide,
an iodide or a di-halide alkyl precursor. For example, in some
implementations, the halogen-containing hydrocarbon precursor is an
alkyl halide. In some embodiments, the halogen-containing
hydrocarbon precursor is a polymer containing the reactive halogen.
For example, in some implementations the halogen-containing
hydrocarbon precursor is a polyoligonucleotide containing the
reactive halogen.
[0097] This highly controllable, tunable property was unattainable
with prior techniques, which are limited to specific types of
functional groups. Moreover, exciton properties with well-defined
divalent defects have not been previously investigated due to
issues relating to the reactivity and stability of precursors (see
Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem. 5:840-845; see also Ghosh, S. et al. (2010) "Oxygen doping
modifies near-infrared band gaps in fluorescent single-walled
carbon nanotubes," Science 330:1656-1659; Zhang, Y. et al. (2013)
"Propagative Sidewall Alkylcarboxylation that Induces Red-Shifted
Near IR Photoluminescence in Single-Walled Carbon Nanotubes," J.
Phys. Chem. Lett. 4:826-830). In FIG. 21, nine exemplary
fluorescent quantum defect systems with continuously tunable
near-infrared PL and surface functionalities are shown. In some
implementations, the sp.sup.3 defects were created in a pristine
carbon nanostructure during the reacting process. Additional
exemplary structures that were synthesized in accordance with
disclosed methodologies are listed in Table 4, demonstrating the
superior chemical and optical tunability of the disclosed synthetic
quantum system.
[0098] By trapping excitons at localized potential wells due to the
quantum defects, it is believed that the excitons respond
sensitively to chemical events occurring at the defect site due to
the amplification effects of the nanotube acting as an antenna
(FIG. 23). The nanotube antenna harvests light efficiently and
channels the generated excitons to the defect site, where the
excitons recombine to produce near-infrared PL encoding the
chemical information at the functional groups. This conclusion is
supported by titration experiments in which H.sup.+ is detected
with both monovalent (6,5)-SWCNT-C.sub.6H.sub.4NH.sub.2, and
divalent (6,5)-SWCNT>C.sub.6H.sub.3NH.sub.2 defects. We find
that, as the amine moiety switches between the protonated and
deprotonated states, the defect PL was shifted by .about.13 meV.
This pH switching was not observed in defects that do not contain
amines, including --C.sub.6H.sub.5 and >C.sub.6H.sub.4,
confirming the localized nature and the high chemical selectivity
of the fluorescent quantum defects.
[0099] The near-infrared emitters synthesized in accordance with
the disclosed methodologies include a carbon nanostructure (e.g,
SWCNTs) comprising sp.sup.3 defects in a carbon lattice thereof
(created via reaction with a halogen-containing hydrocarbon
precursor), and a functional group covalently bonded to the
sp.sup.3 defects to produce fluorescent defects that emit
near-infrared radiation (e.g., having wavelengths between about 800
nm and about 2500 nm). In accordance with disclosed embodiments,
the near-infrared emitters may be functionalized with a monovalent
alkyl group, a divalent alkyl group, a monovalent aryl group, or a
divalent aryl group. For example, in some embodiments, the
functional group is --(CH.sub.2).sub.n(CF.sub.2).sub.mX, wherein n
is an integer between 0 and 17, and wherein m is an integer between
0 and 17, and wherein X is CH3, CF3, NH2, N+(CH2CH3)2, or COOH. In
other embodiments, the functional group is
--(CH.sub.2).sub.nCH.sub.3, wherein n is an integer between 0 and
10.
TABLE-US-00004 TABLE 4 Alkyl/aryl halides used in this study and
their defect photoluminescence. ##STR00009## E.sub.11 E.sub.11-
.DELTA.E (6,5)-SWCNT-R (nm) (nm) (meV) Source of Precursor --X
Non-functionalized 979 -- -- -- --CH.sub.3 980 1094 132 Sigma
Aldrich I --CH.sub.2CH.sub.2CH.sub.2CH.sub.3 984 1099 132 Sigma
Aldrich I --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.3 981
1096 133 Sigma Aldrich I
--CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.3 980 1097 135
Sigma Aldrich Br --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.3
980 1099 137 Oakwood chemical I
--CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2COOH 980 1102 140 Sigma
Aldrich Br --CH.sub.2CH.sub.2CH.sub.2CF.sub.3 981 1101 140 Santa
Cruz Biotech. I --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.3 979 1104
143 Aurum Pharmatech LLC. I --CH.sub.2CH.sub.2CF.sub.3 981 1110 147
Sigma Aldrich I --CH.sub.2CH.sub.2CH.sub.2CH.sub.2CF.sub.2CF.sub.3
980 1107 146 Matrix Scientific I --CH.sub.2CF.sub.3 982 1114 150
Sigma Aldrich I --CH.sub.2CF.sub.2CF.sub.2CF.sub.3 980 1114 152
Pfaltz and bauer I ##STR00010## 980 1121 159 Sigma Aldrich I
##STR00011## 984 1127 160 AstaTech, Inc. I ##STR00012## 979 1121
160 Enamine LLC I >CH.sub.2 (.sup.12C) 979 1125 164 Sigma
Aldrich I.sub.2 >CH.sub.2 (.sup.13C) 980 1125 163 Cambrige
Isotope I.sub.2 ##STR00013## 979 1125 164 Hit2lead I ##STR00014##
979 1129 168 Sigma Aldrich I ##STR00015## 980 1131 169 TCI I
##STR00016## 980 1133 171 Spectra Group Limited Inc I.sub.2
--CH.sub.2CH.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.3 983 1137 170
Sigma Aldrich I
--CH.sub.2CH.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.3
983 1139 173 Sigma Aldrich I --CHF.sub.3 979 1138 177 Sigma Aldrich
I ##STR00017## 980 1145 182 Combiphos catalysts, INC I
--CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.3
979 1152 190 Sigma Aldrich I ##STR00018## 986 1162 190 Sigma
Aldrich I.sub.2 --CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.3
981 1155 190 Sigma Aldrich I --CF.sub.2CF.sub.2CF.sub.2CF.sub.3 979
1155 193 Sigma Aldrich I --CF.sub.3 980 1158 194 Sigma Aldrich I
>CF.sub.2 980 1164 200 SynQuest Lab I.sub.2
EXPERIMENTAL METHODS
Example 1
[0100] Aqueous Dispersions of Individual SWCNT Crystals
[0101] SWCNTs (HiPco batch #194.3 (Rice University; or CoMoCAT
SG65i Lot #000-0036, SouthWest NanoTechnologies, Inc.) were
stabilized by 1 wt. % sodium dodecyl sulfate (Sigma Aldrich,
.gtoreq.98.5%) in deuterium oxide (D.sub.2O, Cambridge Isotope
Laboratories, Inc., 99.8%) by tip ultrasonication (Misonix) at 35
W, 10.degree. C. in a stainless steel beaker for 2 hours, followed
by ultracentrifugation with an Optima LE-80K Ultracentrifuge
(Beckman Coulter) at 170,499 g for 2 hours to remove bundled
nanotubes and residual catalysts. The individually dispersed SWCNTs
were sorted for high purity (6,5)-SWCNTs using gel chromatography
(Liu, H. et al. (2011) "Large-scale single-chirality separation of
single-wall carbon nanotubes by simple gel chromatography," Nat.
Commun. 2), or using the aqueous two phase-assisted separation (Ao,
G. et al. (2014) "DNA-Controlled Partition of Carbon Nanotubes in
Polymer Aqueous Two-Phase Systems," J. Am. Chem. Soc.
136:10383-10392). The samples were diluted to an optical density of
0.1 at the E.sub.11 absorption peak of (6,5)-SWCNTs in 1 wt. % SDS
in D.sub.2O. The concentrations of HiPco and CoMoCAT were
determined with a calibration curve from correlated optical density
and thermogravimetric analysis. The concentration of
chirality-enriched solutions was calculated based on the extinction
coefficient previously determined by Zheng et al. (Zheng, M. &
Diner, B. A. (2004) "Solution Redox Chemistry of Carbon Nanotubes,"
J. Am. Chem. Soc. 126:15490-15494).
[0102] Synthetic Creation of Fluorescent Quantum Defects in
SWCNTs
[0103] Sodium bicarbonate (EMP Chemicals, ACS grade), acetonitrile
(Signal Aldrich, 99.9%) and alkyl halides were added sequentially
to each SWCNT solution, which was kept in a capped glass vial
covered by aluminum foil. Acetonitrile was used as a co-solvent for
the alkyl halide. Sodium dithionite (Sigma Aldrich, 85%) was then
added to the mixture and stirred with a magnetic stir bar at room
temperature. For aryl defects, only aryl-containing iodides are
utilized and the reaction was triggered by optically exciting the
E.sub.22 transition of the nanotubes for single valent groups. The
degree of functionalization was controlled by adjusting the
relative amounts of reagents. The reaction was monitored at various
times by UV-Vis-NIR absorption and fluorescence spectroscopy.
[0104] In Situ UV-Vis-NIR Absorption and Photoluminescence
Spectroscopy
[0105] The reactions were monitored in situ using a Lambda 1050
UV-Vis-NIR spectrophotometer (Perkin Elmer), which is equipped with
both a PMT detector and an extended InGaAs detector, and a NanoLog
spectrofluorometer (Horiba Jobin Yvon). For fluorescence
spectroscopy, the samples were excited with a 450 W Xenon source
dispersed by a double-grating monochromator. Excitation-emission
maps and fluorescence spectra were collected using a liquid-N.sub.2
cooled linear InGaAs array detector on a 320 mm imaging
spectrometer. The spectrofluorometer was calibrated against NIR
emission lines of a pencil-style neon spectral calibration lamp
(Newport).
[0106] Resonant Raman Scattering and X-Ray Photoelectron
Spectroscopy
[0107] The SWCNTs were precipitated out from solution and deposited
on glass slides for Raman scattering or gold-coated silicon
substrates for XPS measurement. XPS was taken with Kratos Axis 165
at 25.degree. C. and 175.degree. C. under an ultrahigh vacuum
(<1.times.10.sup.-8 Torr). Raman spectra were measured on a
LabRAM ARAMIS Raman microscope (Horiba Scientific). The samples
were excited with a He--Ne (632.8 nm) laser or a 532 nm laser at a
power density of 0.014-0.14 mW .mu.m.sup.-2. Each spectrum was
obtained by averaging the data collected from three different
spots. Absorption and PL spectra were fitted with Voigt functions
using PeakFit software v4.12. No baseline correction was applied
during the fitting for PL while a linear background correction was
used for the E.sub.22 absorption.
[0108] Creation of Alkylated Fluorescent Quantum Defects
[0109] Our starting material was (6,5)-SWCNTs approximately 0.75 nm
in diameter and 500 nm in length (or 125 unit cells) on average.
Note that our chemistry readily extends to other nanotube
chiralities. However, (6,5)-SWCNT was chosen for some testing due
to its synthetic abundance and established literature.
[0110] The (6,5)-SWCNTs have intrinsic absorption and
photoluminescence peaks at 979 nm (E.sub.11) and 568 nm (E.sub.22),
which arise from their excitonic transitions (FIG. 2) (O'Connell,
M. J. (2002) "Band Gap Fluorescence from Individual Single-Walled
Carbon Nanotubes," Science 297:593-596). Covalent attachment of
perfluorinated hexyl groups to the nanotubes produced a bright
defect PL peak (E.sub.11.sub.-) at 1155 nm. The observed peak was
redshifted from the parent nanotube PL (E.sub.11) by 177 nm
(.DELTA.E=190 meV), and the full width at half-maximum (FWHM) of
the peak increased from 37 meV to 69 meV. This new feature arose
within minutes of the start of the reaction, and reached the
maximum after about 12 minutes and then plateaued in about 25
minutes. The bright feature remained stable over at least nine
months under ambient conditions (FIG. 2, Panel c).
[0111] Utilizing the disclosed system and methodologies, the
chemical synthesize of a new series of quantum emitters was
demonstrated from semiconducting SWCNTs of the same chirality
through molecular engineering of covalently attached functional
groups.
[0112] As noted above, (6,5)-SWCNTs were utilized in various
embodiments and testing. However, the disclosed methodologies
readily extend to various SWCNT species. For example, .DELTA.E data
of twelve SWCNT species functionalized with perfluorinated hexyl
group is provided in Table 5:
TABLE-US-00005 TABLE 5 Quantum defect near-infrared emitters
synthesized from --CF.sub.2(CF.sub.2).sub.4CF.sub.13 tailored
SWCNTs of different chiralities. The energy difference between
E.sub.11 and E.sub.11.sup.- emission is denoted as .DELTA.E. Chiral
angle diameter Chirality (deg) (nm) E.sub.11 (nm) E.sub.11.sup.-
(nm) .DELTA.E (meV) (5,4) 26.3 0.62 842 1027 265 (6,4) 23.4 0.69
879 1082 264 (7,3) 17 0.71 999 1190 198 (9,1) 5.21 0.76 926 1127
239 (6,5) 27 0.76 979 1152 190 (8,3) 15.3 0.78 955 1169 238 (7,5)
24.5 0.83 1032 1206 173 (8,4) 19.1 0.84 1112 1284 149 (7,6) 27.5
0.90 1133 1291 134 (9,4) 17.48 0.916 1114 1270 137 (11,1) 4.32
0.916 1277 1487 137 (10,3) 12.73 0.936 1260 1445 126
[0113] This new class of synthetic quantum systems shows
molecular-specific optical and electronic properties that are
distinctly different from existing nanostructures. Given the rich
molecular moieties and recent experimental advances in synthesis
and sorting of single-chirality SWCNTs (Tu, X. et al. (2009) "DNA
sequence motifs for structure-specific recognition and separation
of carbon nanotubes," Nature 460:250-253; Sanchez-Valencia, J. R. e
et al. (2014) "Controlled synthesis of single-chirality carbon
nanotubes," Nature 512:61-64), a large variety of near-infrared
quantum emitters may be readily designed and chemically created for
numerous applications, such as in vivo bioimaging and sensing
applications.
Example 2
[0114] Purification of (6,5)-SWCNTs.
[0115] (6,5)-SWCNT enriched samples were isolated from CoMoCAT
SWCNTs (SG65i, lot no. SG65i-L39, Southwest Nanotechnologies) by
aqueous two-phase separation (ATP) (Ao, G. et al. (2014)
"DNA-Controlled Partition of Carbon Nanotubes in Polymer Aqueous
Two-Phase Systems," J. Am. Chem. Soc. 136:10383-10392) using
single-stranded DNA (TCT(CTC).sub.2TCT, Integrated DNA
Technologies). The DNA was precipitated from solution by sodium
thiocyanate (Sigma Aldrich, 98%) and removed after ATP. The
remaining SWCNTs were then suspended in 1 wt/v % sodium dodecyl
sulfate (Sigma Aldrich, .gtoreq.98.5%) in D.sub.2O (Cambridge
Isotope Laboratories, Inc., 99.8%). The optical density of the
solution was adjusted to 0.06 at the (6,5) E.sub.11 transition for
subsequent optical studies. The concentration of the SWCNT
solutions was calculated based on the molar absorptivity of
(6,5)-SWCNTs, determined by Zheng et al. (Zheng, M. & Diner, B.
A. (2004) "Solution Redox Chemistry of Carbon Nanotubes," J. Am.
Chem. Soc. 126:15490-15494).
[0116] Light Activated Arylation.
[0117] A small aliquot of aryl halide in 0.16% v/v acetonitrile
(Acros organics, HPLC grade, 99.9%) was added to the
chirality-enriched SWCNTs in a molar ratio of 10:1 (SWCNT carbon).
In order to avoid the potential PL fluctuation by pH change, the
solution pH was adjusted to 8 by adding 7.6 mM NaHCO.sub.3 (EMD
chemicals, HPLC grade). The SWCNT solutions were irradiated with
monochromator-selected light (10 nm slit width) from a 450 W Xenon
arc lamp. The power density was measured with an optical power
meter (Newport 1916-C) and silicon detector (Newport 918-SL-OD3).
The reactions were protected from ambient light throughout the
experiments. The evolution of defect PL was monitored through a
NanoLog spectrofluorometer (Horiba Jobin Yvon) using a
liquid-N.sub.2 cooled InGaAs array. The spectral resolution
corresponded to 10 nm for the emission detection channel.
[0118] Spectroscopic Characterization.
[0119] The SWCNT PL was characterized with a NanoLog
spectrofluorometer. The SWCNTs were excited at their E.sub.22
transition (565 nm) at a power of 7.5 mW to obtain the PL spectra
with an integration time of 0.5 s. UV-Vis-NIR absorption spectra
were obtained with a spectrophotometer equipped with a broadband
InGaAs detector (Lambda 1050, PerkinElmer). The path length of
absorption measurements was 10 mm. The Raman spectra were obtained
under 532 nm excitation using a confocal Raman microscope (LabRAM
ARAMIS, Horiba Jobin Yvon). Duo scan mode guaranteed that the
measured spectra were averaged data from a 20.times.20 .mu.m.sup.2
area rather than using only a single point. For each sample, 10
data scans were taken at different regions of the sample.
[0120] Density Functional Theory Calculations.
[0121] Geometry optimization was performed for a 10 nm (6,5)-SWCNT
and iodobenzene using DFT at the B3LYP/3-21G level of theory,
implemented in the Gaussian 09 software package. Solvent effects
were included by creating a solute cavity via a set of overlapping
spheres in the framework of the polarizable continuum model using
the integral equation formalism variant (IEFPCM) (Tomasi, J. et al.
(1999) "The IEF version of the PCM solvation method: an overview of
a new method addressed to study molecular solutes at the QM ab
initio level," J. Mol. Struct.: THEOCHEM 464:211-226). Water
(c=78.3553) was chosen as the solvent media. To study the
electronic coupling effects between (6,5)-SWCNT and physisorbed
iodobenzene with 3.3 .ANG. intermolecular distance, single point
calculation was performed using the same functional and basis set.
The density of states was plotted using the Multiwfn software.
[0122] Light-Triggered Creation of Fluorescent Quantum Defects.
[0123] The light-activated chemistry was conducted by mixing
aqueous suspensions of (6,5)-SWCNTs with 4-iodoaniline dissolved in
acetonitrile, adjusting the pH to 8 using sodium bicarbonate, and
then irradiating the solution with 565 nm light. (6,5)-SWCNTs
feature three sharp absorption peaks at 980 nm, 565 nm, and 345 nm,
known as the first (E.sub.11), second (E.sub.22), and third
(E.sub.33) excitonic transitions between the van Hove singularities
(Bachilo, S. M. (2002) "Structure Assigned Optical Spectra of
Single-Walled Carbon Nanotubes," Science 298:2361-2366). In this
system, only (6,5)-SWCNTs absorb the 565 nm light due to the
E.sub.22 electronic transition, while the 4-iodoaniline is
transparent at this wavelength, as shown by the respective
absorption spectra of these materials (FIG. 24, Panel b).
[0124] The progress of this light-induced reaction was monitored
using in situ photoluminescence (PL) spectroscopy. To minimize the
effect of PL measurement on the reaction, a short integration time
(0.5 s) was used to obtain the single excitation PL spectra. While
pristine (6,5)-SWCNTs fluoresce at 980 nm (E.sub.11), exposure to
the aryl iodide reactant and 565 nm light induces a new PL peak
(Etc) at 1130 nm arising from the implanted quantum defects (FIG.
24, Panel b) (Piao, Y. et al. (2013) "Brightening of carbon
nanotube photoluminescence through the incorporation of sp3
defects," Nat. Chem 5(10):840-845; Kwon, H. et al. (2016)
"Molecularly Tunable Fluorescent Quantum Defects," J. Am. Chem.
Soc. 138:6878-6885). This new emission feature is attributed to the
radiative recombination of trapped excitons at local aryl quantum
defects (Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem 5(10):840-845; Hartmann, N. F. et al. (2016)
"Photoluminescence Dynamics of Aryl sp3 Defect States in
Single-Walled Carbon Nanotubes," ACS Nano 10(9):8355-8365).
[0125] During 10 minutes of continuous irradiation, E.sub.11.sub.-
continuously increased while the Eu emission diminished (FIG. 25).
Excitation-emission maps of the pristine and functionalized
(6,5)-SWCNT samples demonstrate that the E.sub.11 and
E.sub.11.sup.- emission peaks are correlated with the E.sub.22
transition of the (6,5)-SWCNT (FIG. 26, Panel a). This new defect
emission was accompanied by an increase in the Raman D/G ratio of
the functionalized (6,5)-SWCNTs (FIG. 27), which confirms the
covalent attachment of aryl groups to the sp.sup.2 carbon lattice
(Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem 5(10):840-845). Irradiation of the SWCNT solution alone or by
adding just sodium bicarbonate (without 4-iodoaniline) does not
generate the defect PL (FIG. 28).
[0126] It was found that this light-driven creation of aryl quantum
defects is significantly more efficient than the alternative
arylation method using diazonium chemistry (Piao, Y. et al. (2013)
"Brightening of carbon nanotube photoluminescence through the
incorporation of sp3 defects," Nat. Chem 5(10):840-845). After
light irradiation for only 10 minutes, the E.sub.11.sub.- emission
is already brighter than E.sub.11 (FIG. 26). This high defect
creation efficiency may be due to electron-transfer (from the
photoexcited SWCNT) promoted generation of aryl radicals.
[0127] Calculating the Reaction Rate of the Light Activated
Arylation Reaction
[0128] A diffusion limited exciton contact-quenching model
(Miyauchi, Y. et al. (2013) "Brightening of excitons in carbon
nanotubes on dimensionality modification," Nat. Photonics
7:715-719) was used to calculate the reaction rate of the light
activated arylation reaction based on the results from the
continuous irradiation experiment. The number of photons (N.sub.11)
emitted from the E.sub.11 state is related to the PL intensity of
E.sub.11 (I.sub.11) by N.sub.11.apprxeq.aI.sub.11, where a is a
constant. Under continuous irradiation, the E.sub.11.sub.- to
E.sub.11 PL intensity ratio, I.sub.11.sub.-/I.sub.11 (t), is
proportional to the number of fluorescent quantum defects at
reaction time t. N.sub.11 is proportional to the PL quantum yield
(.eta..sub.11) and the number of E.sub.11 excitons generated after
photoabsorption (N.sub.abs). The number of E.sub.11 photons in the
unfunctionalized SWCNTs (No) can be calculated by:
N.sub.0=N.sub.abs.eta..sub.11. eq. 1
[0129] Considering the diffusion of photogenerated 1D excitons and
successive trapping by the local defect state (E.sub.11.sup.-), the
number of photons emitted from the E.sub.11.sub.- state
(N.sub.11.sub.-) is expressed as:
N 11 - = N abs .eta. 11 - k dif k i + k dif n 11 - n q + n p + n 11
- eq . 2 ##EQU00001##
in which .eta..sub.11.sub.- is the PL quantum yield of a single
fluorescent aryl defect site; k.sub.dif is the effective decay rate
of the Eu excitons due to exciton diffusion and successive trapping
at the local quenching sites (including intrinsic quenching sites,
physisorbed aryl molecules, and aryl defects); and n.sub.q,
n.sub.p, and n.sub.11- are the number of defects on the SWCNT,
induced by intrinsic quenching sites, physisorption of aryl iodide,
and fluorescent quantum defects, respectively. The factor k.sub.i
is the effective decay rate for all possible mechanisms of exciton
recombination other than the diffusion-limited mechanism. In the
present calculation, the contribution of k.sub.i
(k.sub.i<<k.sub.dif) was ignored, and therefore
k.sub.dif(k.sub.i+k.sub.dif).about.1. Only the trapped E.sub.11
exciton at a local defect can radiatively decay as E.sub.11.sub.-
PL.
[0130] Therefore, by combining eq. 1 and 2, eq. 3 is obtained as
follows:
N 0 N 11 - = .eta. 11 .eta. 11 - n q + n p + n 11 - n 11 - eq . 3
##EQU00002##
[0131] Meanwhile, the light activated arylation of SWCNTs may be
expressed as:
SWCNT ( sp 2 carbon ) + ARI -> SWCNT ArI ( physisorbed ) eq . 4
SWCNT ArI -> hv SWCNT - Ar ( sp 3 defect ) eq . 5
##EQU00003##
[0132] The rate constant of aryl iodide (ArI) physisorption to the
SWCNT sidewall (eq. 4) is defined as k.sub.p and the rate constant
of covalent attachment of physisorbed ArI as an sp.sup.3 aryl
defect is defined as k.sub.c. Thereby, eq. 3 may be re-written
using the rate constants of the chemical reactions:
N 0 N 11 - = .eta. 11 .eta. 11 - n q + k p t + k c t k c t eq . 6
##EQU00004##
[0133] Considering the linear correlation between the number of
photons and the detected PL intensity, eq. 7 is obtained:
I o I 11 - = .eta. 11 .eta. 11 - ( n q k c 1 t + k p k c + 1 ) eq .
7 ##EQU00005##
[0134] By fitting the time dependent intensity ratio with eq. 7
(FIG. 29), it was derived that
(kp/kc)(.eta..sub.11/.eta..sub.11.sub.-) is .about.8.6 and
(n.sub.q/k.sub.c)(.eta..sub.11/.eta..sub.11.sub.-) is .about.77.
The literature values of .eta..sub.11.sub.- and n.sub.q (4
quenching defects in a 0.36 .mu.m long SWCNT) were adapted for the
calculations (Hertel, T. et al. (2010) "Diffusion Limited
Photoluminescence Quantum Yields in 1-D Semiconductors:
Single-Walled Carbon Nanotubes," ACS Nano 4(12):7161-7168).
[0135] Additionally, the correlation plotted in FIG. 30 (Panel b),
FIG. 31 (Panel b), and FIG. 32, and the reaction rate of the light
activated reaction was obtained from the following series of
equations:
N 11 ( t ) = N abs .eta. 11 * eq . 8 .eta. 11 * .varies. k 1 D ( T
) D ( T ) 1 ( n q + n p + n 11 - ) 2 eq . 9 I 11 - ( t ) I 11 ( t )
= .eta. 11 - k dif k 1 + k dif n 11 - n q + n p + n 11 - [ C n q +
n p + n 11 - ] - 2 eq . 10 .varies. n 11 - ( n q + n p + n 11 - )
eq . 11 .apprxeq. n 11 - n q , where n q >> n p + n 11 - eq .
12 ##EQU00006##
in which N.sub.11 and .eta..sub.11* are the number of photons
emitted from E.sub.11 state and the En quantum yield in
functionalized SWCNT; C in eq. 10 accounts for the temperature
dependent radiative decay rate of 1D excitons (km); and D is the
diffusion constant of 1D excitons.
[0136] If the first term, n.sub.q in eq. 11 is significantly larger
than n.sub.p+n.sub.11.sub.-, the intensity ratio I.sub.11.sub.-
(t)/I.sub.11(t) is proportional to the number of fluorescent
quantum defects at the reaction time t. The fitting of experimental
results (FIG. 29) confirms that the assumption is valid during the
initial reaction time. The number of fluorescent quantum defects at
reaction time t corresponds to the product of the reaction rate
(k.sub.c) and t. Based on this model, we can determine from the
experimental data that the rate constant of this light-induced
arylation reaction (k.sub.c) is 0.098 defects.mu.m.sup.-1min.sup.-1
at 7.5 mW of 565 nm light (FIG. 29).
[0137] Photochemical Reaction Mechanism
[0138] In contrast to the high reaction rate under 565 nm light,
the arylation chemistry is thermally inert and does not occur in
the absence of light. When the bulk solution temperature was heated
at 70.degree. C. for 1 h with protection from light, no reaction
occurred, as shown by the absence of the defect E.sub.11.sup.- PL
(FIG. 26, Panels a and c). The slight decrease in the Eu PL
intensity after heating can be attributed to physisorbed aryl
halide (Cognet et al. (2007) "Stepwise quenching of exciton
fluorescence in carbon nanotubes by single-molecule reactions,"
Science 316:1465-1468) and SWCNT aggregation (Wang, D & Chen,
L. (2007) "Temperature and pH-Responsive Single-Walled Carbon
Nanotube Dispersions," Nano Lett. 7(6):1480-1484). However, once
the heated solution was exposed to light, the reaction immediately
evolved (FIG. 30).
[0139] Given that only (6,5)-SWCNTs absorb 565 nm light in this
system (FIG. 24, Panel b), it was verified that SWCNTs were the
source of photo-reactivity. The (6,5)-SWCNT solution was
continuously irradiated for 10 min at selected wavelengths ranging
from ultraviolet (UV) to the near-IR. The reaction was found to
strongly depend on the wavelength of light used to drive the
reaction (FIG. 31, Panel a). To quantitatively compare at each
wavelength, we normalized I.sub.11.sub.-/I.sub.11 ratios after 10
min irradiation, which are correlated with the number of
fluorescent quantum defects created by the reaction via the
excitation fluence. The results indicate that reaction rate closely
follows the absorption spectrum of (6,5)-SWCNTs, with the greatest
rate of reaction occurring at the wavelength where the irradiating
light resonates with the E.sub.22 and E.sub.33 electronic
transitions of the (6,5)-SWCNTs. These observations unambiguously
confirm that the SWCNT itself is targeted by light to drive the
reaction. Interestingly, for irradiation wavelengths longer than
700 nm, no defect PL evolved. The molar extinction coefficient of
(6,5)-SWCNTs is the highest at 980 nm (FIG. 24, Panel b) among the
selected irradiation wavelengths. Despite this, the bonding
reaction does not occur by excitation at 980 nm and similar photon
fluxes, which indicates that the photon energy at this wavelength
is too low to overcome the reaction barrier. This strong dependence
on the exciting photo-energy is a hallmark characteristic of
photochemistry that involves electron transfer.
[0140] To further verify the electron transfer nature of this
photochemistry, a mixture of 4-iodoaniline and (6,5)-SWCNTs was
excited with 565 nm light at various photon fluences spanning over
two orders of magnitude. At each irradiation power,
I.sub.11.sub.-/I.sub.11 increased linearly (R.sup.2=0.999) with
exposure time (FIG. 32), indicating a stable and nearly constant
reaction rate within the observed time period. Even at an
irradiation power reaching 0.03 mW, which accounts for just 0.4% of
the typical power utilized for this study (7.5 mW), the
light-activated arylation reaction still takes place, though at a
slower rate. The reaction rate (k.sub.c at any irradiation power
can be obtained by applying the aforementioned diffusion limited
1D-0D kinetic model to the fluence-dependent PL evolution results
(FIG. 32). In doing so, it was determined that was linear
(R.sup.2=0.999) with the irradiation power (FIG. 31, Panel b). This
threshold free, linear relationship with the fluence further
supports a photochemical rather than photothermal mechanism for the
reaction between SWCNTs and 4-iodoaniline upon irradiation. The
Stark-Einstein law states that for each photon of light absorbed by
a chemical system, only one molecule is activated for subsequent
reaction, and therefore the photochemistry reaction rate is
proportional to the number of incident photons of a given
frequency. In contrast, such a linear relationship does not exist
in the case of the photothermal effect where optically-induced
heating is used to activate the reaction. Under low photon fluence,
the photogenerated heat would be inadequate to drive the reaction
thermally, whereas photochemically even a single photon can
overcome the reaction barrier by pumping the electron to a
sufficiently high energy level.
[0141] As shown by the data and experiments, a reaction mechanism
provides for photoinduced electron transfer between the SWCNT and
the aryl halide (FIGS. 31, Panel c, and FIG. 33). For (6,5)-SWCNTs,
strong light absorption from the valence to conduction bands occurs
between the van Hove singularities. Upon absorption of a photon
that resonates with the electronic transitions of the SWCNT, the
photoinduced electron in the valence band can then be transferred
to the lowest unoccupied molecular orbital (LUMO) of the
physisorbed 4-iodoaniline to produce a 4-iodoaniline radical anion,
which dissociates into an iodine anion and an aniline radical. The
aniline radical readily grafts to the SWCNT, converting an sp.sup.2
hybridized carbon to sp.sup.a. Such an electron transfer mediated
decomposition of aryl halides and subsequent covalent
functionalization to the sp.sup.2 carbon lattice has been studied
by electrochemical methods (Koefoed, L. et al. (2017) "Covalent
Modification of Glassy Carbon Surfaces by Electrochemical Grafting
of Aryl Iodides," Langmuir 33(13):3217-3222). As shown by the
present experiments, the photoinduced electron behaves like an
electrochemically injected electron to drive this photochemical
reaction.
[0142] This electron-transfer mechanism is further supported by
density functional theory (DFT) calculations (FIG. 31, Panel c, and
FIG. 33), in which it was determined that the LUMO of iodobenzene
lies 0.58 eV above the valence band of the (6,5)-SWCNT, but was
lower than the second van Hove singularities of the conduction band
(De Blauwe, K. et al. (2010) "Combined experimental and ab initio
study of the electronic structure of narrow-diameter single-wall
carbon nanotubes with predominant (6,4),(6,5) chirality," Phys.
Rev. B 82:125444; Hertel, T. et al. (2010) "Diffusion Limited
Photoluminescence Quantum Yields in 1-D Semiconductors:
Single-Walled Carbon Nanotubes," ACS Nano 4(12):7161-7168). Given
the relatively low energy of the (6,5)-SWCNT's valence band, the
uphill transfer of an electron from this energy level to the
iodobenzene LUMO is unlikely to occur at room temperature, which is
in agreement with the dark control wherein no functionalization was
observed. To realize the proposed electron transfer, electrons must
be promoted from the valence band to higher excited states. This
finding is consistent with the observed wavelength-dependent
reaction efficiency. Although the E.sub.22 to E.sub.11 relaxation
is the fast and dominating pathway for an excited SWCNT, a small
possibility of intermolecular electron transfer is sufficient to
drive the covalent functionalization due to the photochemical
nature. Such conclusion is in agreement with the observed reaction
rate (0.098 defects .mu.m.sup.-1 min.sup.-1), which is relatively
insignificant compared to the number of photons absorbed by the
nanotube. It is also noted that the electronic transition of the
SWCNTs cannot occur by raising temperature alone, as the energy
barrier for electron transfer is high (178 kJ/mol), which explains
the absence of reaction even at raised solution temperatures when
light was not applied (FIGS. 26 and 30).
[0143] This light-activated reaction of SWCNTs is not limited to
aryl iodides. Fluorescent quantum defects may be created by
irradiation from virtually any aryl halide precursor except aryl
fluoride (FIG. 34). The reaction efficiency follows the trend of
the leaving group ability, with I>Br>Cl>F. Although the
E.sub.11 and E.sub.11.sub.- vary around their peak positions
slightly (by 7.5 meV) due to the different dielectric environments,
the energy difference between E.sub.11 and E.sub.11.sub.-
(.DELTA.E.sub.optical) remains unchanged for aryl defects of the
same chemical nature (e.g., 157 meV for
(6,5)-SWCNT-C.sub.6H.sub.5).
[0144] Molecularly Tunable Defect Emission
[0145] The defect PL is molecularly tunable by changing the
terminating groups of the aryl halides (Table 6 and FIG. 35). Table
6 presents the tunability of the defect PL wavelength. By changing
the terminating groups of the aryl halides, 32 meV tunability is
achieved in .DELTA.E.sub.optical for (6,5)-SWCNTs. The molecular
tunability is linearly correlated to the electron withdrawing
ability of the functional groups, which can be quantified using the
Hammett constant (.sigma.) (Hansch, C. et al. (1977) "Substituent
constants for correlation analysis," J. Med. Chem. 20:304) (FIG.
35), which is consistent with previously demonstrated diazonium
chemistry (Piao, Y. et al. (2013) "Brightening of carbon nanotube
photoluminescence through the incorporation of sp3 defects," Nat.
Chem 5(10):840-845). Moreover, this arylation chemistry benefits
from a wider choice of functional groups as compared to diazonium
chemistry (e.g., enabling the incorporation of amine functional
groups, which could be used to link nanotubes to complex molecules
that cannot be prepared as diazonium salts).
TABLE-US-00006 TABLE 6 Tunable defect PL in (6,5)-SWCNTs strongly
depends on the Hammett substituent constant (.sigma.) of the
terminating moieties of the aryl defects. Hammett E.sub.11
E.sub.11.sup.- .DELTA.Eoptical Moiety constant (.sigma.).sup.a (nm)
(nm) (meV) 4-N(CH.sub.3).sub.2 -0.83 990 1130 155 4-NH.sub.2 -0.66
990 1132 157 3,5-(NH.sub.2).sub.2 -0.32 990 1141 166
4-NHC.sub.2H.sub.4CONH.sub.2 -0.18 985 1128 160 H 0 984 1134 167
1,2,3,4,5-F.sub.5.sup.b 0.83 984 1146 178
2,4-(NO.sub.2).sub.2.sup.b 1.37 985 1157 187 3,5-(NO.sub.2).sub.2
1.42 983 1154 187 .sup.aThe Hammett constants of the aryl moieties
were calculated as a summation of .sigma..sub.ortho,
.sigma..sub.meta and .sigma..sub.para values. .sup.bThe moieties in
the ortho position were assumed to be 0.75 times their effect in
the para position, .sigma..sub.ortho = 0.75 .sigma..sub.para
(Charton, M. (1960) "The Application of the Hammett Equation to
Ortho-Substituted Benzene Reaction Series," Can. J. Chem.
38(12):2493-2499).
[0146] This photochemical mechanism enables precise control of the
chemical creation of quantum defects with light. To demonstrate
this control, a light-switching experiment was conducted to show
how the reaction can be readily modulated. The light was switched
ON for 2 min, followed by 3 min OFF. This alternating on-off cycle
was repeated for up to 45 times. The evolution of the SWCNT PL
during the first four on-off cycles are shown in FIG. 36, in which
the ratio of I.sub.11.sub.-/I.sub.11 increases significantly during
the light exposure periods but stops completely when the light is
turned off, demonstrating step-wise reaction progress these
conditions. Furthermore, the slope of the PL evolution during each
ON cycle is constant, indicating a consistent reaction rate at
different cycles within the studied time window.
[0147] Programmably Coded Quantum Emitters
[0148] As demonstrated herein, fluorescent quantum defects can be
programmably patterned into individual SWCNT by the disclosed light
activated reaction. Many polymers are known to wrap the carbon
nanotube tightly due to the strong non-covalent interactions with
the carbon nanotube surface and therefore are used to disperse
tubes in various solvent. However, those polymers are not able to
introduce quantum defect to the carbon nanotube due to the lack of
reactive groups. By synthetically incorporating halide containing
moieties into those polymer chains with controlled distance, these
modified polymers create quantum defect patterns in the carbon host
using the disclosed light activated reaction of the present
invention. This is possible because the polymer wrapping brings the
aryl halide to the vicinity of the nanotube surface, which enables
the electron transfer and covalent bonding formation upon the
resonant irradiation of the carbon nanotube.
[0149] In support thereof, a DNA sequence containing two binding
sites was designed that can be activated by light. DNA is a
versatile and low-cost biopolymer that can be easily synthesized to
have desired sequence and modification. Here, a sequence (5'-TTA
TAT TAT ATT-3') (SEQ ID NO: 1) was adopted that is known to
selective wrap (6,5)-SWCNTs and replaced the 4.sup.th and 7.sup.th
thymine (T) from the 5' end with 5-IododexoyUridine (5I-dU) to
generate a new sequence (5'-TTA (5I-dU)AT (5I-dU)AT ATT-3') (SEQ ID
NO: 2). Other suitable oligonucleotide sequences include: 5'-GTT
GT(5I-dU) GT(5I-dU) G-3' (SEQ ID NO: 3); 5'-TT(5I-dU) ATT TA(5I-dU)
TTA T-3' (SEQ ID NO: 4); or 5'-T(5I-dU)A TTA T(5I-dU) A TTG TT-3'
(SEQ ID NO: 5). We note that T and 5I-dU have similar structure, so
the replacement was less likely to affect the interaction between
the carbon nanotube and the DNA. Indeed, the absorption spectrum
and photoluminescence spectrum of the DNA dispersed (6,5)-SWCNT
showed the carbon nanotube was stabilized as individual particle
(FIG. 37). While the DNA dispersed (6,5)-SWCNTs fluoresce at 998 nm
(E.sub.11), exposure to the 565 nm light induced a new PL peak
(E.sub.11.sub.-) at 1160 nm, which is 173.5 meV red-shifted from
the E.sub.11 emission (FIG. 38). The appearance of the new defect
PL confirms the creation of quantum defects by the photochemical
reaction between the carbon nanotube surface and the 5I-dU moieties
in the DNA sequences that wrapped the nanotube. The relative
position of two adjacent defect sites is controlled by the distance
between the two 5I-dU moieties in a DNA, and therefore can be
programmed synthetically.
[0150] Thus, programmably coded quantum emitters and the
photochemical creation of molecularly tunable, aryl quantum defects
in semiconducting SWCNTs have been demonstrated. The reaction is
efficiently driven by optically exciting the host in the presence
of a halide-containing aryl molecule. As shown, the chemistry does
not depend on the solution temperature, but strongly correlates
with the photon energy used to drive the reaction. This
photochemical mechanism was further supported by DFT calculations,
which revealed a consistent energy diagram. As demonstrated herein,
the reaction occurs by electron transfer from the excited nanotube
to a physically absorbed aryl halide, producing an aryl radical
that locally bonds to the carbon lattice in a covalent manner.
Unlike photothermal effects, this photochemical mechanism makes it
possible to spatially confine the reaction.
[0151] As also demonstrated, the quantum defects may be
synthetically created stepwise with light. This photochemistry
provides for the ability to photolithographically pattern
molecularly tunable, fluorescent quantum emitters for applications,
e.g., in near-IR imaging (Hong, G. et al. (2015) "Carbon
Nanomaterials for Biological Imaging and Nanomedicinal Therapy,"
Chem. Rev. 115(19):10816-10906), chemical sensing (Kwon, H. et al.
(2015) "Optical Probing of Local pH and Temperature in Complex
Fluids with Covalently Functionalized, Semiconducting Carbon
Nanotubes," J. Phys. Chem. 119(7):3733-3739; Shiraki, T. et al.
(2016) "Near infrared photoluminescence modulation of single-walled
carbon nanotubes based on a molecular recognition approach," Chem.
Commun. (Camb.) 52(88):12972-12975), photonics (He, X. et al.
(2017) "Tunable room-temperature single-photon emission at telecom
wavelengths from sp3 defects in carbon nanotubes," Nat. Photonics
11:577-582), and solid-state quantum electronics (Aharonovich, I.
et al. (2016) "Solid-state single photon emitters," Nat. Photonics
10:631-641).
[0152] In some experiments, (6,5)-SWCNT were utilized as a model
system. Other CNTs suitable for use with the present invention
include, e.g., (6,5)-SWCNTs, (10,6)-SWCNTs, (10,9)-SWCNTs, (10,
3)-SWCNTs, (6,4)-SWCNTs, and (7,5)-SWCNTs. In addition, the
methodologies are extendable to other CNTs having different
chiralities, e.g., when the energy levels of the semiconductor host
and the halide-containing aryl molecule match such that electron
transfer is possible. Energy match for this photochemical chemistry
enables selective functionalization of a specific semiconductor
host chirality within a mixture, (e.g., SWCNTs, which is preferred
for nanotube sorting). Given the demonstrated quantitative
photochemical nature, such light control also addresses the
challenge of controlling the local atomic configurations of quantum
defects (He, X. et al. (2017) "Low-Temperature Single Carbon
Nanotube Spectroscopy of sp3 Quantum Defects." ACS Nano
10.1021/acsnano.7b03022; Shiraki, T. et al. (2017) "Near infrared
photoluminescence modulation by defect site design using aryl
isomers in locally functionalized single-walled carbon nanotubes,"
Chem. Commun. 53:12544-12547).
[0153] Thus, while the invention has been described in connection
with exemplary embodiments and experiments thereof, it will be
understood that it is capable of further modifications and this
application is intended to cover any variations, uses, or
adaptations of the invention following, in general, the principles
of the invention and including such departures from the present
disclosure as come within known or customary practice within the
art to which the invention pertains and as may be applied to the
features hereinbefore set forth.
[0154] All identified publications and references are herein
incorporated by reference to the same extent as if each individual
publication was specifically and individually indicated to be
incorporated by reference in its entirety.
Sequence CWU 1
1
5112DNAArtificial Sequencesynthetically generated polynucleotide
1ttatattata tt 12212DNAArtificial Sequencesynthetically generated
polynucleotide (n is 5-iododexoyuridine (5I-dU))misc_featuren is
5-IododexoyUridine (5I-dU) 2ttanatnata tt 12310DNAArtificial
Sequencesynthetically generated polynucleotide (n is
5-iododexoyuridine (5I-dU))misc_featuren is 5-IododexoyUridine
(5I-dU) 3gttgtngtng 10413DNAArtificial Sequencesynthetically
generated polynucleotide (n is 5-iododexoyuridine
(5I-dU))misc_featuren is 5-IododexoyUridine (5I-dU) 4ttnatttant tat
13514DNAArtificial Sequencesynthetically generated polynucleotide
(n is 5-iododexoyuridine (5I-dU))misc_featuren is
5-IododexoyUridine (5I-dU) 5tnattatnat tgtt 14
* * * * *